int reflect(){
int i,j,k=-1;
double L,af1,af2;
double L1,L2,L3,D,pl,tL,L4;
for (i=0;i<n;i++)
if (dot(s,s+st,a[i])>eps){
L1=Dis(s,a[i]);
L2=Dis(s+st,a[i]);
L3=Dis(s,s+st);
af1=acos((L1*L1+L3*L3-L2*L2)/2/L1/L3-eps);
D=L1*sin(af1);
if (D<r[i]-1e-8){
pl=L1*L1-D*D;
if (k==-1 || pl<L){
k=i;
L=pl;
}
}
}
if (k==-1) return 0;
if (m==10) printf("etc.\n");else printf("%d ",k+1);
L1=Dis(s,a[k]);
L2=Dis(s+st,a[k]);
L3=Dis(s,s+st);
af1=acos((L1*L1+L3*L3-L2*L2)/2/L1/L3-eps);
D=L1*sin(af1);
pl=sqrt(L1*L1-D*D+eps);
tL=sqrt(r[k]*r[k]-D*D+eps);
pl-=tL;
node ts,tst,v1,v2,v3;
ts=s+mul(st,pl/L3);
if (fabs(D)<eps){
s=ts;
st=mul(st,-1);
return 1;
}
// printf("%.5lf %.5lf %.5lf\n",ts.x,ts.y,ts.z);
L4=L1*((L1*L1+r[k]*r[k]-pl*pl)/2/L1/r[k]);
v1=ts-a[k];
v2=mul(v1,L4/r[k]);
v3=a[k]+v2;
v1=v3-s;
v2=v1+v1;
tst=(s+v2)-ts;
s=ts;
st=tst;
//printf("%.5lf %.5lf %.5lf\n",st.x,st.y,st.z);
return 1;
}
main(){
int i,j,k,n,m,dim,hyper;
while (scanf("%d %d",&n,&m)==2 && n+m){
hyper = 1;
for (i = n,dim = 0;i > 1;i >>= 1,++dim)
if (i>1 && i%2 != 0)
hyper = 0;
if (m*2 != n*dim) hyper = 0;
for (i = 0;i < n;++i)
deg[i] = 0;
while (m--) {
scanf("%d %d",&j,&k);
if (Dis(j,k)!=1)
hyper = 0;
if (j < 0 || j >= n) hyper = 0;
else ++deg[j];
if (k < 0 || k >= n) hyper = 0;
else ++deg[k];
}
for (i = 0;i < n;++i)
if (deg[i] != dim) hyper = 0;
puts(hyper?"YES":"NO");
}
}
