#include"iostream"
#include"string.h"
#include"vector"
using namespace std; 
int vis[105],B[105];
vector<int>V[105];
bool Match(int id)
{
    for(int ge=0;ge<V[id].size();ge++)
    {
        int t=V[id][ge];
        if(vis[t]==1)continue;          /*?aà?±ê??ê?òò?aóDμY1é*/
        vis[t]=1;
        if(B[t]==-1||Match(B[t]))       /*è?1?óò±?μ??ü??óD?￥??￡??ò?ü?òμ?ì?′úμ??íà?ò?*/ 
        {
            B[t]=id;
            return 1;
        }
    }
    return 0;
}
int main()
{
    int M,N;
    cin>>M>>N;
    int t1,t2;
    memset(B,-1,sizeof(B));
    while(cin>>t1>>t2&&t1!=-1&&t2!=-1)
    {
        V[t1].push_back(t2-M);
    }
    int sum=0;
    for(int i=1;i<=M;i++)
    {
        memset(vis,-1,sizeof(vis));
        if(Match(i))sum++;
    }
    cout<<sum<<"\n";
}