#include <cstdio>
inline int min(int a, int b) { return a < b ? a : b; }
const int maxn = 100010;
int head[maxn], next[maxn << 1], to[maxn << 1], ecnt, n, m;
int dfn[maxn], scc[maxn], cnt[maxn], scccnt, stk[maxn], low[maxn], idx, top;
inline void addEdge(int f, int t)
{
    ecnt++;
    next[ecnt] = head[f];
    head[f] = ecnt;
    to[ecnt] = t;
}
void tarjan(int x)
{
    dfn[x] = low[x] = ++idx;
    stk[top++] = x;
    for (int i = head[x]; i; i = next[i])
        if (!dfn[to[i]])
            tarjan(to[i]), low[x] = min(low[x], low[to[i]]);
        else if (!scc[to[i]])
            low[x] = min(low[x], dfn[to[i]]);
    if (dfn[x] == low[x])
    {
        scccnt++;
        do
            scc[stk[--top]] = scccnt;
        while (stk[top] != x);
    }
}
int main()
{
    scanf("%d%d", &n, &m);
    for (int i = 0, x, y; i < m; i++)
    {
        scanf("%d%d", &x, &y);
        addEdge(x, y);
    }
    for (int i = 1; i <= n; i++)
        if (!dfn[i]) tarjan(i);
    int ans = 0;
    for (int i = 1; i <= n; i++) cnt[scc[i]]++;
    for (int i = 1; i <= scccnt; i++)
        if (cnt[i] > 1) ans++;
    printf("%d", ans);
    return 0;
}