#include<bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint=modint998244353;
using namespace std;
using ll=long long;
using ul=unsigned long long;
int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1};
int dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};
using Graph=vector<vector<int>>;
int main(){
    int N,M;
    cin>>N>>M;
    set<int>st;
    for(int i=0;i<M;i++){
        int u,v;
        cin>>u>>v;
        st.insert(v);
    }
    cout<<N-st.size()<<endl;
}