q(int*a,int*b){return*a-*b;}i,*x;main(n){scanf("%d",&n);for(;i<n;i++)scanf("%d",&x[i]);qsort(x,n,4,q);n--;for(i=1;i<n;i++)if(x[i-1]-x[i]!=x[i]-x[i+1]||!(x[i-1]-x[i]))break;puts(i-n?"NO":"YES");}