x,a[1<<17],m,M;c(int*a,int*b){x=*a-*b;}main(i){for(;~scanf("%d",a-i);i--);for(qsort(a,-i,4,c);++i;!m|m>x?m=x:0,M<x?M=x:0)x=a[-i]-a[~i];x=!puts(m-M|!M?"NO":"YES");}