#include <bits/stdc++.h>
using namespace std;
int n, m, k, now, a[100005], b[100005], c[100005], d[100005];
signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin >> n >> m >> k;
	for (int i = 1; i <= n; i++) {
		c[i] = i;
	}
	for (int i = 1; i <= m; i++) {
		cin >> a[i] >> b[i];
	}
	for (int i = m; i >= 1; i--) {
		swap(c[a[i]], c[b[i]]);
	}
	now = 1;
	for (int i = 1; i <= m; i++) {
		swap(c[a[i]], c[b[i]]);
		if (c[now] == k) {
			cout << i;
			return 0;
		}
		if (a[i] == now) now = b[i];
		else if (b[i] == now) now = a[i];
	}
	cout << -1;
}
//10 10 9
//1 8
//8 3
//3 4
//4 7
//7 2
//6 2
//9 10
//3 10
//9 3
//6 9