#include <stdio.h>
int main(void){
	int val = 0;
	scanf("%d",&val);
	
	int loc[val];
	for(int i = 0;i < val;i ++){
		scanf("%d",&loc[i]);
	}
	
	for(int i = 0;i < val;i ++){
		for(int j = 0;j < val;j ++){
			if(loc[i] == loc[j]){
				printf("NO");
				return 0;
			}
			if(loc[i] > loc[j]){
				int tmp = loc[i];
				loc[i] = loc[j];
				loc[j] = tmp;
			}
		}
	}
	
	int interval = loc[1] - loc[0];
	for(int i = 2;i < val;i ++){
		if(interval != loc[i] - loc[i - 1]){
			printf("NO");
			return 0;
		}
	}
	printf("YES");
}