1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
#include <bits/stdc++.h>
#include <string>

using namespace std;

typedef long long LL;
typedef long double LD;
typedef pair < int, int > PII;
typedef pair < LL, LL > PLL;
typedef pair < LD, LD > PDD;

#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define st first
#define nd second
#define pb push_back
#define REP(i,a,b) for(int i = (a); i <= (b); i++)
#define FOR(i, n) REP(i, 0, int(n) - 1)
#define pii pair < int, int >
#define ll long long
#define fi first
#define se second
#define mp make_pair
#define vi vector <int>

const int MAXN = 342;
bool G[MAXN][MAXN];
vector<int> g[MAXN], gr[MAXN];
int dep[MAXN], depr[MAXN];
int v1=-1,v2=-1,v3=-1,v4=-1;

int dfs(int w) {
    if(dep[w]) return dep[w];
    FOR(i,g[w].size())
        if(g[w][i] != v1 && g[w][i] != v2 && g[w][i] != v3 && g[w][i] != v4)
            dep[w] = max(dep[w], 1 + dfs(g[w][i]));
    return dep[w];
}

int dfsr(int w) {
    if(depr[w]) return depr[w];
    FOR(i,gr[w].size())
        if(gr[w][i] != v1 && gr[w][i] != v2 && gr[w][i] != v3 && gr[w][i] != v4)
            depr[w] = max(depr[w], 1 + dfsr(gr[w][i]));
    return depr[w];
}

int main()
{
    ios_base::sync_with_stdio(0);
    srand (time(NULL));
        int n = 100, m = 400,k, cnt = 0;
        cin>>n>>m>>k;
        /*while(cnt < m) {
            int a = rand() % n, b = rand() % n;
            if(a != b && G[a][b] == 0) {
                //G[a][b] = 1;
                //G[b][a] = 1;
                g[min(a,b)].pb(max(a,b));
                gr[max(a,b)].pb(min(a,b));
                cnt++;
            }
        }*/
        FOR(i,m) {
            int a,b;
            cin>>a>>b;
            a--; b--;
            g[a].pb(b);
            gr[b].pb(a);
        }
        int odp = 0, odp2 = MAXN;
        FOR(i,n) odp = max(odp, dfs(i));
        FOR(i,n) dfsr(i);


        int threshold;
        FOR(dis, n) {
            int cnt = 0;
            FOR(i,n) if(dep[i] >= dis && depr[i] >= dis) cnt++;
            if(cnt < 54) {threshold = dis; break;}
        }
        vector<int> tolook;
        FOR(i,n) if(dep[i] >= threshold && depr[i] >= threshold) tolook.pb(i);
        //cout<<threshold<<" vertices "<<tolook.size()<<"\n";

        //for(V1=0;V1<tolook.size();V1++) for(V2=V1+1;V2<tolook.size();V2++) for(V3=V2+1;V3<tolook.size();V3++) for(V4=V3+1;V4<tolook.size();V4++) {
        if(k==4) {
            FOR(V1,tolook.size()) REP(V2,V1+1,tolook.size()-1) REP(V3,V2+1,tolook.size()-1) REP(V4,V3+1,tolook.size()-1) {
                v1 = tolook[V1];
                v2 = tolook[V2];
                v3 = tolook[V3];
                v4 = tolook[V4];
                FOR(i,n) dep[i] = 0;
                int temp = 0;
                FOR(i,n) temp = max(temp, dfs(i));
                odp2 = min(temp, odp2);
            }
        }
        else if(k==3) {
            FOR(V1,tolook.size()) REP(V2,V1+1,tolook.size()-1) REP(V3,V2+1,tolook.size()-1) {
                v1 = tolook[V1];
                v2 = tolook[V2];
                v3 = tolook[V3];
                v4 = -1;
                FOR(i,n) dep[i] = 0;
                int temp = 0;
                FOR(i,n) temp = max(temp, dfs(i));
                odp2 = min(temp, odp2);
            }
        }
        else if(k==2) {
            FOR(V1,tolook.size()) REP(V2,V1+1,tolook.size()-1) {
                v1 = tolook[V1];
                v2 = tolook[V2];
                v3 = -1;
                v4 = -1;
                FOR(i,n) dep[i] = 0;
                int temp = 0;
                FOR(i,n) temp = max(temp, dfs(i));
                odp2 = min(temp, odp2);
            }
        }
        else if(k==1) {
            FOR(V1,tolook.size()) {
                v1 = tolook[V1];
                v2 = -1;
                v3 = -1;
                v4 = -1;
                FOR(i,n) dep[i] = 0;
                int temp = 0;
                FOR(i,n) temp = max(temp, dfs(i));
                odp2 = min(temp, odp2);
            }
        }

        if(k == n) cout<<"0\n";
        else cout<<odp2+1<<"\n";
    return 0;
}