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

using i64 = long long;

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    auto solve = [&]() {
        int n, m;
        cin >> n >> m;

        vector<int> a(n);
        for (int i = 0; i < n; i++) {
            cin >> a[i];
        }

        vector<array<int, 2>> edges(m);
        for (auto &[u, v] : edges) {
            cin >> u >> v;
            u--, v--;
        }

        vector<int> pattern{0, 0, 1, 1};

        vector<vector<int>> adj(4 * n);
        vector<int> in(4 * n), len(4 * n), q;

        for (int i = 0; i < 4; i++) {
            for (int u = 0; u < n; u++) {
                if (a[u] == pattern[i]) {
                    len[i * n + u] = 1;
                }
            }
            int j = (i + 1) % 4;
            for (auto [u, v] : edges) {
                for (int rep : {0, 1}) {
                    if (a[u] == pattern[i] && a[v] == pattern[j]) {
                        adj[j * n + v].push_back(i * n + u);
                        in[i * n + u]++;
                    }
                    swap(u, v);
                }
            }
        }

        for (int i = 0; i < 4 * n; i++) {
            if (in[i] == 0) {
                q.push_back(i);
            }
        }
        for (int i = 0; i < q.size(); i++) {
            int u = q[i];
            for (auto v : adj[u]) {
                len[v] = max(len[v], len[u] + 1);
                if (--in[v] == 0) {
                    q.push_back(v);
                }
            }
        }

        if (count(in.begin(), in.end(), 0) != 4 * n) {
            cout << "infinity" << '\n';
            return;
        }

        constexpr int inf = 1e9;
        int ans = inf;

        for (int i = 0; i < 4; i++) {
            ans = min(ans, *max_element(len.begin() + i * n, len.begin() + (i + 1) * n) + 1);
        }

        cout << ans << '\n';
    };
    
    solve();
    
    return 0;
}