#include <stdio.h>
#include <stdlib.h>
#define NMAX 100000
#define FIN "dfs.in"
#define FOUT "dfs.out"

enum colors {WHITE, GRAY, BLACK};

void read();
void DFS();
void DFS_Visit(int u);

int *A[NMAX], prev[NMAX], color[NMAX];
int m, n, count;

void read()
{
     int x, y, i; 
     scanf("%d %d", &n, &m);
     for (i=1; i<=n; ++i) {
         A[i] = (int*)malloc(sizeof(int));
         A[i][0] = 0;
     }
     for (i=1; i<=m; ++i) {
         scanf("%d %d", &x, &y);
         ++A[x][0];
         A[x] = realloc(A[x], (A[x][0]+1)*sizeof(int));
         A[x][A[x][0]] = y;
     }
}

void DFS()
{
     int i;
     for (i=1; i<=n; i++) {
         color[i] = WHITE;
         prev[i] = 0;
     }
     for (i=1; i<=n; ++i)
         if (color[i] == WHITE) {
            DFS_Visit(i);
            ++count;
         }
}

void DFS_Visit(int u)
{
     int i;
     color[u] = GRAY;
     for (i=1; i<=A[u][0]; ++i)
         if (color[A[u][i]] == WHITE) {
                            prev[A[u][i]] = u;
                            DFS_Visit(A[u][i]);
         }
     color[u] = BLACK;
}

int main()
{
    freopen(FIN, "r", stdin);
    freopen(FOUT, "w", stdout);
    read();
    DFS();
    printf("%d", count);
    return 0;
}