#include <stdio.h>
int main(void){
    int N,b;
    int e=0;
    scanf("%d",&N);
    int a[N];
    for(b=0;b<N;b++){
        scanf("%d",&a[b]);
    }
    for(b=0;b<N;b++){
       if(a[b]==a[b+1]){
       e=1;
       break;
       }
       
    }
if(e==0){
    int c=a[0]; 
    for(b=1;b<N;b++){
        if(c>a[b])
        c=a[b];
    }
    int d=100000000;
    for(b=0;b<N;b++){
        if(a[b]==c)
        continue;

         if(d>a[b])
        d=a[b];
    }        
    d-=c;   
    for(b=0;b<N;b++){
        if((a[b]-a[b+1])%d!=0)
        break;
    }
   printf((a[b]-a[b+1])%d==0?"YES":"NO");
}else
printf("NO");
}