#include <stdio.h>

#include <string.h>

#define NMAX 10

int nodp[NMAX];

int nodset[NMAX];

int main(void){

int i,j;

int nodn,siden;

while (scanf("%d%d",江若琳 - ?情路,&nodn,&siden)!=-1){

int setn =0;

int curset = 1;

int accept =1;

int x,y;

       　　  memset(nodp,0,sizeof(nodp));

memset(nodset,猎人和狼的故事,0,sizeof(nodset));

for(i=0;i<siden;i++){

scanf("%d%d",“我们开房吧时尚商务酒店”--有点暧昧,&x,英语脏话精选！（不是教你骂人，是教你听懂别人在骂你！）,&y);

nodp[x]++;

nodp[y]++;

if(nodn<3||x==y||siden<3) accept =0;

if (!accept) continue;

if(nodset[x]){

if(nodset[y]&&nodset[y]!=nodset[x]){

//if x,y have a side with diff set, merge the two

int tmpset =nodset[y];

for(int j =0;j<nodn;j++){

if(nodset[j]==tmpset)

nodset[j]=nodset[x];

}

setn--;

}

else if(nodset[y]==0){

nodset[y] = nodset[x];

}

}

else if(nodset[y]){

nodset[x] = nodset[y];

}

else {

setn++;

nodset[x]=nodset[y]=curset;

curset++;

}

}

//gets(strtmp);

//confirm if only one circle

if(setn!=1){

accept =0;

}

//confirm if extra side outside the circle

for(j = 1;j<=nodn;j++){

if (nodp[j]!=2&&nodp[j]!=0){//nodp[j]!=2

accept =0;

break;

}

}

if(accept)

puts("YES");

else

puts("NO");

//

}

return 0;

}