#include <set>#include <iostream>#include <stdio.h>using namespace std;int main(){ int n,m; while(scanf("%d%d",&n,&m)!=EOF && n!=-1 && m!=-1) { set <int > R_num; set <int > B_num; for(int i=1; i<=m; i++) { int x,y; scanf("%d%d",&x,&y); if(i%2!=0) { R_num.insert(x); R_num.insert(y); if(B_num.find(x)!=B_num.end() ) B_num.erase(x); if(B_num.find(y)!=B_num.end() ) B_num.erase(y); } else { B_num.insert(x); B_num.insert(y); if(R_num.find(x)!=R_num.end() ) R_num.erase(x); if(R_num.find(y)!=R_num.end() ) R_num.erase(y); } } if(B_num.size()==n) printf("YES\n"); else printf("NO\n"); set<int >::iterator iter; for(iter=R_num.begin(); iter!=R_num.end(); iter++) cout << *iter << endl; } return 0;}