/*
HDU 2444 The Accomodation of Students

*/
#include<iostream>
#include<string.h>
#include<vector>
using namespace std;
#define MAXN 202
vector<int>EV[MAXN];
int linker[MAXN];
bool used[MAXN];
int uN;
int matchs[MAXN],cnt[MAXN];
bool dfs(int u)
{
    int i;
    for(i=0;i<EV[u].size();i++)
    {
        int v=EV[u][i];
        if(!used[v])
        {
            used[v]=true;
            if(linker[v]==-1||dfs(linker[v]))
            {
                linker[v]=u;
                return true;
            }    
        }    
    }
    return false;    
}   
int hungary()
{
    int res=0;
    int u;
    memset(linker,-1,sizeof(linker));
    for(u=1;u<=uN;u++)
    {
        memset(used,false,sizeof(used));
        if(dfs(u))  res++;
    }
    return res;    
}  
bool judge(int x,int y)
{
    int i;
    for(i=0;i<EV[x].size();i++)
    {
        if(cnt[EV[x][i]]==0)
        {
            cnt[EV[x][i]]=-1*y;
            matchs[EV[x][i]]=true;
            if(!judge(EV[x][i],-1*y)) return false;
        }   
        else if(cnt[EV[x][i]]==y)  return false; 
    }    
    return true;
}    
bool matched()
{
    int i;
    memset(matchs,false,sizeof(matchs));
    for(i=1;i<=uN;i++)
    {
        if(EV[i].size()&&!matchs[i])
        {
            memset(cnt,0,sizeof(cnt));
            cnt[i]=-1;
            matchs[i]=true;
            if(!judge(i,-1)) return false;
        }    
    }
    return true;    
}     
int main()
{
    int m;
    int i;
    int u,v;
    while(scanf("%d%d",&uN,&m)!=EOF)
    {
        for(i=1;i<=uN;i++)
          if(EV[i].size())  EV[i].clear();
        while(m--)
        {
            scanf("%d%d",&u,&v);
            EV[u].push_back(v);
            EV[v].push_back(u);
        }    
     
         if(matched())
                  printf("%d\n",hungary()/2);
         else  printf("No\n");    
    } 
    return 0;
}