#include<stdio.h>
#include<algorithm>
main(){
    int N;
    scanf("%d",&N);
    int x[100000];
    for(int i = 0;i < N;i++){
        scanf("%d",&x[i]);
    }
    std::sort(x,x+N);
    int dif = x[1]-x[0];
    for(int i = 2;i < N;i++){
        if(!dif || dif!=x[i]-x[i-1]){
            printf("NO\n");
            return 0;
        }
    }
    printf("YES\n");
}