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#include <bits/stdc++.h>
#define ll long long
#define pi pair <int,int>
#define fi first
#define se second
using namespace std;
const int N = 405, M = 1005, INF = (1<<30), MAX_IT = 140000000; 
int n, m, k;
vector <pi> E(M); vector < vector <int> > In(N+1), Out(N+1);
vector <int> Forward(N+2), Backward(N+2), A(N+1), Pos;
ll power(ll n, ll k)
{
	return (k == 0) ? 1 : n * pow(n, k-1);
}
void count_forward_and_backward(int n, vector <bool> &Del)
{
	for (int i = 1; i <= n; i++) 
		Forward[i] = Backward[i] = 0;
	for (int u = 1; u <= n; u++)
		for (int p : In[u])
			if (!Del[p] && !Del[u])
				Backward[u] = max(Backward[u], Backward[p]+1);
	for (int u = n; u >= 1; u--)
		for (int v : Out[u])
			if (!Del[v] && !Del[u])
				Forward[u] = max(Forward[u], Forward[v]+1);
}
int get_answer_for_deleted(int n, int k, vector <bool> &Del)
{
	count_forward_and_backward(n, Del);
	int ans = 0;
	for (int u = 1; u <= n; u++)
		if (!Del[u])
			ans = max(ans, Backward[u] + Forward[u] + 1);
	return ans;
}
int check_all_combinations(int i, int n, int d, int k, vector <int> &A, vector <bool> &Del)
{
	if (d == k)
		return get_answer_for_deleted(n, k, Del);
	if (i+(k-d-1) > n)
		return INF;
	int ans = INF;
	for (int j = i; j <= n; j++) {
		Del[A[j]] = true;
		ans = min(ans, check_all_combinations(j+1, n, d+1, k, A, Del));
		Del[A[j]] = false;
	}
	return ans;
}
void get_rands(int n, int k, vector <int> &R)
{
	for (int i = 0; i < k; i++)
		R[i] = abs(rand()) % n;
}
int solve(int n, int k)
{
	vector <bool> Del(n+1, false);
	if (k <= 1 || power(n, k) * (n+m) <= MAX_IT) {
		for (int i = 1; i <= n; i++)
			A[i] = i;
		return check_all_combinations(1, n, 0, k, A, Del);
	}
	else {
		int ans = get_answer_for_deleted(n, k, Del), cur; vector <int> Rands(k);
		int siz = 0, siz1 = 0; vector <int> Pos, New;
		for (int u = 1; u <= n; u++) {
			//cout << u << " " << Forward[u] << " " << Backward[u] <<endl;
			if (2 * min(Forward[u], Backward[u])+1 >= ans-1) {
				Pos.push_back(u);
				siz++;
				New.push_back(u);
				siz1++;
			}
		}
		//cout << ans << " " << siz << " " << siz1 <<endl;
		int from_new, r, mod = min(k+1, siz1+1);
		for (int it = 0; (n+m) * it < MAX_IT; it++) {
			get_rands(siz, k, Rands);
			if (siz1 > 0) {
				from_new = abs(rand()) % mod;
				//cout << from_new << " " << siz1 <<endl;
				map <int,int> M;
				for (int i = 0; i < from_new; i++) {
					r = siz - siz1 + abs(rand()) % siz1;
					if (M[r] == 0)
						Rands[i] = r, M[r] = 1;
				}
			}
			for (int v : Rands)
				Del[Pos[v]] = true;
			cur = get_answer_for_deleted(n, k, Del);
			for (int v : Rands)
				Del[Pos[v]] = false;
			if (cur < ans) {
				if (ans - cur > 1 || (ans - cur == 1 && (cur - 1 + 2) % 2 == 1)) {
					New.clear();
					siz1 = 0;
					count_forward_and_backward(n, Del);
					for (int u = 1; u <= n; u++) {
						if ((Forward[u] + Backward[u]) != 0 &&
							2 * min(Forward[u], Backward[u])+1 >= cur-1 && 
							2 * min(Forward[u], Backward[u])+1 < ans-1) {
							
							Pos.push_back(u);
							siz++;
							New.push_back(u);
							siz1++;
						}
					}
				}
				mod = min(k+1, siz1+1);
				//cout << "NEW " << cur << " " << ans << " " << siz << " " << siz1 <<endl;
				ans = cur;
			}
		}
		//cout << ans << " " << siz << " " << siz1 <<endl;
		for (int it = 0; it < 1000; it++) {
			get_rands(n, k, Rands);
			for (int v : Rands)
				Del[v] = true;
			ans = min(ans, get_answer_for_deleted(n, k, Del));
			for (int v : Rands)
				Del[v] = false;
		}
		return ans;
	}
}
int main()
{
	srand(time(NULL));
	ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	cin >> n >> m >> k;
	for (int i = 0; i < m; i++) {
		cin >> E[i].fi >> E[i].se;
		In[E[i].se].push_back(E[i].fi);
		Out[E[i].fi].push_back(E[i].se);
	}
	cout << solve(n, k) <<endl;
	/*cout << 300 << " " << 299 << " " << 3 <<endl;
	for (int i = 1; i+1 <= 300; i++)
		cout << i << " " << i+1 <<endl;*/
	return 0;
}