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#include <iostream>
#include <vector>
#include <queue>
#define pb push_back

using namespace std;

typedef vector<vector<int>> graph;

int main() {
	ios_base::sync_with_stdio(0);

	int n, m, k;
	cin >> n >> m >> k;

	graph g(n+2);
	vector<int> deg(n+1, 0);

	int s = 0;
	int a, b;
	for (int i = 0; i < m; i++) {
		cin >> a >> b;
		g[a].pb(b);
		deg[b]++;
	}

	for (int i = 1; i <= n; i++) {
		if (deg[i] == 0) {
			g[s].pb(i);
			deg[i]++;
		}
	}

	vector<int> it(k), d, used;
	for (int i = 1; i <= k; i++) it[k-1] = k;

	const int inf = 1e8;
	queue<int> q;
	int res = inf;

	int end = false;
	while (!end) {
		d.assign(n+1, 0);
		used.assign(n+1, 0);
		for (int i = 0; i < k; i++) d[it[i]] = inf;
		d[s] = -1;
		q.push(s);
		int lres = -1;

		while(!q.empty()) {
			int x = q.front(); q.pop();
			if (d[x] != inf) {
				lres = max(lres, d[x]);

				if (lres >= res) {
					q = queue<int>();
					break;
				}

				for (int y : g[x]) {
					d[y] = max(d[y], d[x]+1);
				}
			}

			for (int y : g[x]) {
				if (++used[y] == deg[y]) q.push(y);
			}
		}

		res = min(res, lres);

		end = true;
		for (int i = k-1; i >= 0; i--) {
			if (it[i] <= n-k+i) {
				it[i]++;
				for (int j = i+1; j < k; j++) it[j] = it[j-1]+1;
				end = false;
				break;
			}
		}
	}

	cout << res + 1 << endl;

	return 0;
}