#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 5;
int n, m, dp[N];
long long ans = 1;
bool vis[N][2], ok;
vector <int> e[N][2];
void dfs1(int x) {
	vis[x][0] = true;
	if (!ok) dp[x] = true;
	if (x == n) ok = true;
	for (int i : e[x][0]) if (!vis[i][0]) dfs1(i);
	if (!ok) dp[x] = false;
}
void dfs2(int x) {
	vis[x][1] = true;
	for (int i : e[x][1]) if (!vis[i][1]) dfs2(i);
}
int main() {
	cin.tie(0) -> sync_with_stdio(false);
	cin >> n >> m;
	for (int i = 1, x, y; i <= m; ++i) {
		cin >> x >> y;
		e[x][0].push_back(y);
		e[y][1].push_back(x);
	}
	dfs1(1);
	dfs2(n);
	if (!ok) {
		cout << 0;
		return 0;
	}
	for (int i = 1; i <= n; ++i) {
		if (!vis[i][0] || !vis[i][1] || dp[i]) continue;
		for (int j : e[i][1]) if (vis[j][0] && vis[j][1]) dp[i] += dp[j];
		int tmp = 0;
		for (int j : e[i][0]) if (dp[j]) ++tmp;
		ans += 1LL * dp[i] * tmp; 
	}
	cout << ans;
}