#include <bits/stdc++.h>using namespace std;const int N = 100 + 5;
const int INF = 0x3f3f3f3f;    int dis[N][N];
int f[N][N];
bool inq[N][N];
vector<int> g1[N], g2[N];int main() {    int n, m, kase = 0;while (scanf("%d %d", &n, &m) == 2 && n) {for (int i = 1; i <= n; i++) {g1[i].clear();g2[i].clear();}memset(dis, INF, sizeof dis);for (int i = 1; i <= n; i++) {dis[i][i] = 0;}for (int i = 1; i <= m; i++) {int u, v;scanf("%d %d", &u, &v);dis[u][v] = 1;g1[u].push_back(v);g2[v].push_back(u);}for (int k = 1; k <= n; k++) {for (int i = 1; i <= n; i++) {for (int j = 1; j <= n; j++) {dis[i][j] = min(dis[i][j], dis[i][k] + dis[k][j]);}}}printf("Network %d\n", ++kase);if (dis[1][2] != INF && dis[2][1] != INF) {memset(f, INF, sizeof f);f[1][1] = 1;queue<int> q1, q2;q1.push(1);q2.push(1);inq[1][1] = true;while (!q1.empty()) {int u1 = q1.front(), u2 = q2.front();q1.pop(); q2.pop();inq[u1][u2] = false;for (int i = 0; i < g1[u1].size(); i++) {int v1 = g1[u1][i];    int cand = f[u1][u2] + (v1 != u2);if (cand < f[v1][u2]) {f[v1][u2] = cand;if (!inq[v1][u2]) {q1.push(v1);q2.push(u2);inq[v1][u2] = true;}}}for (int i = 0; i < g2[u2].size(); i++) {int v2 = g2[u2][i];int cand = f[u1][u2] + (v2 != u1);if (cand < f[u1][v2]) {f[u1][v2] = cand;if (!inq[u1][v2]) {q1.push(u1);q2.push(v2);inq[u1][v2] = true;}}}if (u1 != u2 && f[u1][u2] + dis[u1][u2] - 1 < f[u2][u1]) {f[u2][u1] = f[u1][u2] + dis[u1][u2] - 1;if (!inq[u2][u1]) {q1.push(u2);q2.push(u1);inq[u2][u1] = true;}}}printf("Minimum number of nodes = %d\n", f[2][2]);} else {printf("Impossible\n");}printf("\n");}return 0;
}