#include <map>
#include <set>
#include <array>
#include <cmath>
#include <deque>
#include <bitset>
#include <random>
#include <string>
#include <vector>
#include <cassert>
#include <complex>
#include <iomanip>
#include <iostream>
#include <algorithm>
#include <unordered_map>
#include <unordered_set>

using namespace std;

const int MAXN = 1'000'100;

vector<int> G[MAXN];
vector<int> GT[MAXN];

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);

  int n, m;
  cin >> n >> m;
  vector<pair<int, int>> edges(m);
  for (int i = 0; i < m; ++i) {
    int a, b;
    cin >> a >> b;
    --a;
    --b;
    edges[i] = make_pair(a, b);
    G[a].emplace_back(b);
    GT[b].emplace_back(a);
  }
  vector<bool> reached_from_last(n, false);
  reached_from_last[n - 1] = true;
  deque<int> Q;
  Q.emplace_back(n - 1);
  while (!Q.empty()) {
    int v = Q.front();
    Q.pop_front();
    for (int u : GT[v]) {
      if (!reached_from_last[u]) {
        reached_from_last[u] = true;
        Q.emplace_back(u);
      }
    }
  }
  if (!reached_from_last[0]) {
    cout << 0 << '\n';
    return 0;
  }
  vector<bool> reached_from_first(n, false);
  reached_from_first[0] = true;
  Q.emplace_back(0);
  while (!Q.empty()) {
    int v = Q.front();
    Q.pop_front();
    for (int u : G[v]) {
      if (!reached_from_first[u]) {
        reached_from_first[u] = true;
        Q.emplace_back(u);
      }
    }
  }
  int new_n = 0;
  int new_m = 0;
  vector<bool> good(n);
  for (int i = 0; i < n; ++i) {
    good[i] = reached_from_first[i] && reached_from_last[i];
    new_n += good[i];
  }
  for (auto [a, b] : edges)
    new_m += good[a] && good[b];
  cout << new_m - new_n + 2 << '\n';
  return 0;
}