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

int dfs(vector<vector<int>>& v, vector<int>& dp1,vector<int>&dpn, int node) {
    dp1[node] = 1;

    if (node == n)return dpn[node] = 1;

    if (dpn[node] != -1)return 1;
    
    auto& ret = dpn[node];
    ret = 0;

    for (auto& to : v[node]) {
        ret |= dfs(v, dp1,dpn, to);
    }

    return ret;
}

int ans = 0;
void dfs2(vector<vector<int>>& v,vector<int>&dpn, vector<int>& vis, int node) {
    if (vis[node])return ans++, void();
    vis[node] = 1;

    for (auto& to : v[node]) {
        if (dpn[to] != -1) {
            dfs2(v, dpn, vis, to);
        }
    }

}
signed main() {
    ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);

    cin >> n;
    int m;
    cin >> m;

    vector<vector<int>>v(n+1);
    vector<int>dp1(n + 1,-1),dpn(n+1,-1);
    while (m--) {
        int a, b;
        cin >> a >> b;
        v[a].push_back(b);

    }

    dfs(v, dp1, dpn, 1);

    if (dp1[n] == -1) {
        return cout << "0\n", 0;
    }
    
    vector<int>vis(n + 1);
    dfs2(v, dpn, vis, 1);
    cout <<ans+1 << "\n";
}