#include using namespace std; int n, m; int a[100], b[100]; int main() { scanf("%d%d", &n, &m); for (int i = 1; i <= n; ++i) a[i] = b[i] = 0; for (int i = 1; i <= m; ++i) { int x, y; scanf("%d%d", &x, &y); if (a[x] < y && b[y] < x) { if (a[x] > 0) b[a[x]] = 0; if (b[y] > 0) a[b[y]] = 0; a[x] = y; b[y] = x; } } int ans = 0; for (int i = 1; i <= n; ++i) { if (a[i] == 0) ++ans; if (b[i] == 0) ++ans; } printf("%d", ans); return 0; }