#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<vector<int>> adj(n), radj(n);
        for (int i = 0; i < m; i++) {
            int u, v;
            cin >> u >> v;
            u--, v--;
            adj[u].push_back(v);
            radj[v].push_back(u);
        }

        auto work = [&](int s, auto &adj) {
            vector<int> vis(n);
            auto dfs = [&](auto dfs, int u) -> void {
                vis[u] = true;
                for (auto v : adj[u]) {
                    if (!vis[v]) {
                        dfs(dfs, v);
                    }
                }
            };
            dfs(dfs, s);
            return vis;
        };

        auto vis = work(0, adj);
        auto rvis = work(n - 1, radj);

        if (!vis[n - 1]) {
            cout << "0\n";
            return;
        }

        int V = 0, E = 0;
        for (int i = 0; i < n; i++) {
            V += vis[i] && rvis[i];
        }
        for (int u = 0; u < n; u++) {
            for (auto v : adj[u]) {
                E += vis[u] && rvis[u] && vis[v] && rvis[v];
            }
        }

        cout << E - V + 2 << '\n';
    };
    
    solve();
    
    return 0;
}