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#include <cstdio>
#include <cstdlib>
#include <vector>
#include <map>
#include <algorithm>
#include <set>
#include <time.h>
#include <queue>

typedef long long int64;

using namespace std;

struct vertex_t {
	vector<int> adj_in;
	vector<int> adj_out;
};

const int RAND = 32000;

inline int longest_path(vector<vector<int> >& g, vector<int>& cache, vector<int>& bad) {
	int gmax = 0;
	for (int i = 0; i < g.size(); ++i) {
		if (find(bad.begin(), bad.end(), i) != bad.end()) {
			continue;
		}
		int max = 1;
		for (vector<int>::iterator it = g[i].begin(); it != g[i].end(); it++) {
			if (find(bad.begin(), bad.end(), *it) != bad.end()) {
				continue;
			}
			int len = cache[*it] + 1;
			if (len > max) {
				max = len;
			}
		}
		cache[i] = max;
		if (max > gmax) {
			gmax = max;
		}
	}
	return gmax;
}

int main () {
	int m, n, k;
	scanf("%d %d %d", &n, &m, &k);
	vector<vector<int> > graph(n, vector<int>());
	for (int i = 0; i < m; ++i) {
		int from, to;
		scanf("%d %d", &from, &to);
		graph[to - 1].push_back(from - 1);
	}
	int min_path = 1000;
	vector<int> cache(n, 0);
	vector<int> bad(k, 0);
	if (k == 1) {
		for (int i = 0; i < n; ++i) {
			bad[0] = i;
			int res = longest_path(graph, cache, bad);
			if (res < min_path) {
				min_path = res;
			}
		}
	}
	else if (k == 2) {
		for (int i = 0; i < n; ++i) {
			bad[0] = i;
			for (int j = i + 1; j < n; ++j) {
				bad[1] = j;
				int res = longest_path(graph, cache, bad);
				if (res < min_path) {
					min_path = res;
				}
			}
		}
	}
	else {
		for (int i = 0; i < RAND; ++i) {
			for (int j = 0; j < k; ++j) {
				bad[j] = rand() % n;
			}
			int res = longest_path(graph, cache, bad);
			if (res < min_path) {
				min_path = res;
			}
		}
	}
	printf("%d\n", min_path);
	return 0;
}