#include <stdio.h>
#include <stdlib.h>

int func(const void *a, const void *b){
    return *(int *)a - *(int *)b;
}

int main(){
    int N, i, sub, cnt = 0;
    int kamo[100000];

    scanf("%d\n", &N);
    for(i = 0; i < N; i++){
        scanf("%d ", &kamo[i]);
    }
    qsort(kamo, N, sizeof(int), func);
    sub = kamo[1] - kamo[0];
    for(i = 1; i < N; i++){
        //printf("%d\n", sub);
        if(sub == (kamo[i] - kamo[i - 1]) && sub != 0){
            cnt++;
        }else{
            printf("NO\n");
            break;
        }
        sub = kamo[i] - kamo[i - 1];
    }
    if(cnt == N - 1){
        printf("YES\n");
    }

    return 0;
}