#include <bits/stdc++.h>
typedef long long ll;
using namespace std;

int n;

vector<vector<int> > mul(vector<vector<int> > a, vector<vector<int> > b){
    vector<vector<int> > ret(n, vector<int> (n, 0));
    for(int i=0;i<n;i++) 
        for(int j=0;j<n;j++) 
            for(int k=0;k<n;k++) 
                ret[i][j] |= a[i][k] & b[k][j];
    return ret;
}

vector<vector<int> > pow(vector<vector<int> > a, ll t){
    vector<vector<int> > ret(n, vector<int> (n, 0));
    for(int i=0;i<n;i++) ret[i][i] = 1;
    while(t > 0){
        if(t & 1) ret = mul(ret, a);
        a = mul(a, a);
        t >>= 1;
    }
    return ret;
}
int main() {
    ll m, t;
    cin >> n >> m >> t;
    vector<vector<int> > G(n, vector<int> (n, 0));

    int a, b;

    for(int i=0;i<m;i++){
        cin >> a >> b;
        G[b][a] = 1;
    }

    G = pow(G, t);

    int ans = 0;
    for(int i=0;i<n;i++) ans += G[i][0];
    cout << (ans ? ans : -1) << endl;

    return 0;
}