#include <cstdio>
#include <vector>

void DFS(auto& visited, auto& list, int start)
{
        visited[start] = true;

        for(int v : list[start])
        {
                if(!visited[v])
                {
                        DFS(visited, list, v);
                }
        }
}

int main()
{
        int n, m;
        std::scanf("%d%d", &n, &m);

        std::vector<std::vector<int>> list(n + 1);
        std::vector<char> visited(n + 1, false);
        for(int i = 0; i < m; ++i)
        {
                int x, y;
                std::scanf("%d%d", &x, &y);

                list[x].push_back(y);
        }

        int res = 0;
        for(int node = 1; node <= n; ++node)
        {
                if(!visited[node])
                {
                        ++res;
                        DFS(visited, list, node);
                }
        }

        std::printf("%d\n", res);
}