#include <cstdio>
#include <vector>

using namespace std;

#define FIN "mesaj4.in"
#define FOUT "mesaj4.out"

#define MAXN 100000

int N, M, R;

vector <int> V[MAXN];

void solve()
{

}

int main()
{
    int i, x, y;

    freopen(FIN, "r", stdin);
    freopen(FOUT, "w", stdout);

    scanf("%d%d", &N, &M);

    for (i = 1; i <= N; ++ i)
    {
        scanf("%d%d", &x, &y);

        V[x].push_back(y);
    }

    solve();

    printf("-1\n", R);
}