#include<iostream>
#include<vector>
#define endl '\n'
using namespace std;
typedef long long ll;
int n,k;
vector<int> g[510];
int match[510]={};
bool find(int i)
{
for(int j=0;j<g[i].size();j++)
{
int &m=match[g[i][j]];
if(m==0 || m!=i && find(m))
{
m=i;
return true;
}
}
return false;
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cin>>n>>k;
for(int i=0;i<k;i++)
{
int a,b;
cin>>a>>b;
g[a].push_back(b);
}
int ans=0;
for(int i=1;i<=n;i++)
if(find(i))
ans++;
cout<<ans<<endl;
}
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