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#include <bits/stdc++.h>
#define pb push_back
#define mp make_pair
#define f first
#define s second

using namespace std;

const int MAX_N = 1e6 + 9;
const int LOG_MAX_N = 22;

typedef long long lli;
typedef pair<int, int> PII;

bitset<MAX_N> bypassed;
bitset<MAX_N> cycleBeneath;

vector<int> G[MAX_N];
vector<int> component;

int myComponent[MAX_N];

lli D[MAX_N];
lli F[MAX_N];
lli t = 1;
lli zero = 1;

int LCA[MAX_N][LOG_MAX_N];
int P[MAX_N];

int depth[MAX_N];

int valStarting[MAX_N];
int valEnding[MAX_N];
int valFinal[MAX_N];
int bypass[MAX_N];
int totalCycles = 0;

int currentComponent = 1;
int mainComponent = -1;
bool cycleInCurrentComponent = false;

int n, m;
int sol;

int findLCA(int a, int b)
{
    //cout << "LCA " << a <<" i " << b << ": ";
    if(depth[a] != depth[b])
    {
        if(depth[a] > depth[b])
            swap(a, b);

        for(int i = LOG_MAX_N; i >= 0; --i)
        {
            if(LCA[b][i] != 0 && depth[LCA[b][i]] >= depth[a])
                b = LCA[b][i];
        }
    }

    if(a == b)
    {
        //cout << a << endl;
        return a;
    }

    for(int i = LOG_MAX_N; i >= 0; --i)
    {
        if(LCA[a][i] != LCA[b][i])
        {
            a = LCA[a][i];
            b = LCA[b][i];
        }
    }

    //cout << LCA[a][1] << endl;

    return LCA[a][1];
}

void DFS_components(int v)
{
    D[v] = 1;
    myComponent[v] = currentComponent;

    for(int i = 0; i < G[v].size(); ++i)
    {
        int u = G[v][i];

        if(D[u] == 0)
        {
            depth[u] = depth[v] + 1;
            P[u] = v;
            DFS_components(u);
        }
        else if(F[u] == 0)
        {
            if(cycleInCurrentComponent == false)
            {
                cycleInCurrentComponent = true;
                ++totalCycles;
            }
        }
    }

    F[v] = 1;

    return;
}

void DFS_findCycles(int v)
{
    D[v] = ++t;

    for(int i = 0; i < G[v].size(); ++i)
    {
        int u = G[v][i];

        if(D[u] <= zero)
        {
            DFS_findCycles(u);
            if(cycleBeneath[u])
                cycleBeneath[v] = true;
        }
        else if(F[u] <= zero)
        {
            cycleBeneath[v] = true;
            ++valStarting[v];
            ++valEnding[u];
            ++totalCycles;
        }
    }

    F[v] = ++t;
}

void DFS_calculate(int v)
{
    D[v] = ++t;

    for(int i = 0; i < G[v].size(); ++i)
    {
        int u = G[v][i];

        if(D[u] <= zero)
        {
            DFS_calculate(u);
            valFinal[v] += valFinal[u] - valEnding[u];
        }
    }

    valFinal[v] += valStarting[v];

    F[v] = ++t;

    return;
}

void DFS_calculateBypass(int v)
{
    D[v] = ++t;

    for(int i = 0; i < G[v].size(); ++i)
    {
        int u = G[v][i];

        if(D[u] <= zero)
        {
            DFS_calculateBypass(u);
        }
        else if(F[u] > zero && cycleBeneath[u] && valFinal[v] != 0 && valFinal[u] != 0)
        {
            int lca = findLCA(v, u);
            if(P[v] != lca)
                bypass[P[v]] = depth[lca] + 1;
            if(P[u] != lca)
                bypass[P[u]] = depth[lca] + 1;
        }
    }

    F[v] = ++t;

    return;
}

void DFS_bypass(int v)
{
    D[v] = ++t;

    for(int i = 0; i < G[v].size(); ++i)
    {
        int u = G[v][i];

        if(D[u] <= zero)
        {
            DFS_bypass(u);
            if(bypass[u] != -1)
            {
                if(bypass[v] == -1)
                    bypass[v] = bypass[u];
                else
                    bypass[v] = min(bypass[v], bypass[u]);
            }
        }
    }

    if(bypass[v] != -1 && bypass[v] <= depth[v])
        bypassed[v] = true;

    F[v] = ++t;

    return;
}

int main()
{
    scanf("%d%d", &n, &m);

    fill(bypass, bypass + n + 1, -1);
    depth[0] = -1;

    int a, b;

    for(int i = 0; i < m; ++i)
    {
        scanf("%d%d", &a, &b);

        G[a].pb(b);
    }

    for(int i = 1; i <= n; ++i)
    {
        if(D[i] == 0)
        {
            DFS_components(i);
            ++currentComponent;
        }

        if(totalCycles >= 2)
        {
            printf("0\n\n");
            return 0;
        }

        else if(cycleInCurrentComponent == true)
        {
            mainComponent = currentComponent - 1;
            cycleInCurrentComponent = false;
        }
    }

    if(totalCycles == 0)
    {
        printf("NIE\n");
        return 0;
    }

    totalCycles = 0;
    zero = t;

    for(int i = 1; i <= n; ++i)
    {
        LCA[i][0] = i;
        LCA[i][1] = P[i];
    }

    for(int j = 2; j <= LOG_MAX_N; ++j)
    {
        for(int i = 1; i <= n; ++i)
        {
            LCA[i][j] = LCA[LCA[i][j - 1]][j - 1];
        }
    }

    for(int i = 1; i <= n; ++i)
    {
        if(myComponent[i] == mainComponent)
            component.pb(i);
    }

    for(int i = 0; i < component.size(); ++i)
    {
        int root = component[i];

        if(D[root] <= zero)
            DFS_findCycles(root);
    }

    /*for(int i = 0; i < n; ++i)
    {
        cout << i << ": " << cycleBeneath[i] << endl;
    }*/

    zero = t;

    for(int i = 0; i < component.size(); ++i)
    {
        int root = component[i];

        if(D[root] <= zero)
            DFS_calculate(root);
    }

    zero = t;

    for(int i = 0; i < component.size(); ++i)
    {
        int root = component[i];

        if(D[root] <= zero)
            DFS_calculateBypass(root);
    }

    zero = t;

    for(int i = 0; i < component.size(); ++i)
    {
        int root = component[i];

        if(D[root] <= zero)
            DFS_bypass(root);
    }

    for(int i = 1; i <= n; ++i)
        if(valFinal[i] == totalCycles && !bypassed[i])
            ++sol;

    printf("%d\n", sol);

    for(int i = 1; i <= n; ++i)
        if(valFinal[i] == totalCycles && !bypassed[i])
            printf("%d ", i);

    return 0;
}