hdu2444

 #include <stdio.h>
 #include <string.h>
 #define  black 1
 #define  white -1
 int already[];
 int in[];
 int gr[][];
 int n;
 int v[];
 int pf,pe;

 int dfs(int a,int color){
     v[a]=color;
     int i;
     int sign;
     for(i=;i<=n;++i){
         if(i==a) continue;
         if(gr[a][i]&&v[i]==){
             if((sign=dfs(i,-color))==-) return -;
         }else if(gr[a][i]&&v[i]==color){
             return -;
         }
     }
     return ;
 }
 int judge(){
     int i;
     int sign;
     memset(v,,sizeof(v));
     for(i=;i<=n;++i){
         if(==v[i]){
             if((sign=dfs(i,black))==-) return -;
         }
     }
     return ;
 }

 int find(int a){
     int i;
     for(i=;i<=n;++i){
         if(v[i]==white&&gr[a][i]&&!in[i]){
             in[i]=;
             if(already[i]==||find(already[i])){
                 already[i]=a;
                 return ;
             }
         }
     }
     return ;
 }
 int main(){
     int m;
     int i,j;
     int res;
     while(~scanf("%d%d",&n,&m)){
         res=;
         memset(gr,,sizeof(gr));
         while(m--){
             scanf("%d%d",&i,&j);
             gr[i][j]=;
             gr[j][i]=;
         }
         if(judge()==-){
             printf("No\n");
             continue;
         }

         memset(already,,sizeof(already));
         for(i=;i<=n;++i){
             memset(in,,sizeof(in));
             if(v[i]==black)
                 if(find(i))
                     res++;
         }
         printf("%d\n",res);
     }
     return ;
 }