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

int N;
int *x;
void read() {
	scanf("%d\n", &N);
	x = (int *)malloc(sizeof(int)*N);
	for (int i = 0; i < N; i++) {
		scanf("%d", &x[i]);
	}
}
int main() {
	read();
	for (int i = N - 1; i >= 0; i--) {
		for (int j = 0; j < i; j++) {
			if (x[j] > x[j + 1]) {
				int k = x[j];
				x[j] = x[j + 1];
				x[j + 1] = k;
			}
		}
	}
	for (int i = 0; i < N - 1; i++) {
		if (x[i] == x[i + 1]) {
			printf("NO");
			return 0;
		}
	}
	int width = x[1] - x[0];
	if (N == 2) {
		printf("YES");
		return 0;
	}
	for (int i = 2; i < N; i++) {
		if (x[i] - x[i - 1] != width) {
			printf("NO");
			return 0;
		}
	}
	printf("YES");
	return 0;
}