#include <stdio.h>
#include <algorithm>
int main(){
    //input
    int N;
    scanf("%d",&N);

    int x[100000];
    for (int i = 0;i < N;i++){
        scanf("%d",&x[i]);
    }

    //sort array x
    std::sort(x,x+N);

    //diffrence of x_i and x_i+1
    int d = x[1]-x[0];
    if (d == 0){
        printf("NO\n");
        return 0;
    }

    //search
    for (int i = 0;i <= N-2;i++){
        if (x[i+1]-x[i] != d){
            printf("NO\n");
            return 0;
        }
    }
    printf("YES\n");
    return 0;
}