#include <bits/stdc++.h>
#define eb emplace_back
#define mt make_tuple
#define mp make_pair
#define fi first
#define se second

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
bool Mbe;

const int N = 1e6 + 5;

int n, m, d[N], vs[N], vt[N];
vector<int> g[N], ig[N];
pi e[N];

void dfs(int u) {
	vs[u] = 1;
	for (int v : g[u]) {
		if (vs[v]) continue;
		dfs(v);
	}
}

void solve() {
	cin >> n >> m;
	for (int i = 1, u, v; i <= m; i++)
		cin >> u >> v, g[u].eb(v), ig[v].eb(u), e[i] = mp(u, v);
	dfs(1), memcpy(vt, vs, sizeof(int) * (n + 1));
	dfs(n); for (int i = 1; i <= n; i++) vs[i] &= vt[i];
	if (!vs[n]) return cout << 0 << '\n', void();
	int c1 = 0, c2 = 0;
	for (int i = 1; i <= n; i++) c1 += vs[i];
	for (int i = 1; i <= m; i++) c2 += (vs[e[i].fi] && vs[e[i].se]);
	cout << c2 - c1 + 2 << '\n';
}

bool Med;
int main() {
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	cerr << (&Mbe - &Med) / 1048576.0 << " MB\n";
	#ifdef FILE
		freopen(".in", "r", stdin);
		freopen(".out", "w", stdout);
	#endif
	int T = 1;
	// cin >> T;
	while (T--) solve();
	cerr << (int)(1e3 * clock() / CLOCKS_PER_SEC) << " ms\n";
	return 0;
}