#include <stdio.h>

int n, x[100000];

int y[100000];

void sort(int l, int r) {
	if(r - l < 2) { return; }
	
	int m = (r + l) / 2;
	sort(l, m);
	sort(m, r);
	
	int ll = l, rr = m, cc = l;
	while(ll < m || rr < r) {
		bool flag;
		     if(rr == r) { flag = true;  }
		else if(ll == m) { flag = false; }
		else if(x[ll] <= x[rr]) { flag = true; }
		else { flag = false; }
		
		if(flag) { y[cc++] = x[ll++]; }
		else     { y[cc++] = x[rr++]; }
	}
	
	for(cc = l; cc < r; cc++) { x[cc] = y[cc]; }
	
	return;
}

int main() {
	scanf("%d", &n);
	for(int i = 0; i < n; i++) { scanf("%d", &x[i]); }
	
	sort(0, n);
	
	int d = x[1] - x[0];
	bool ans = false;
	if(d != 0) {
		ans = true;
		for(int i = 1; i < n; i++) {
			ans &= (x[i] - x[i - 1] == d);
		}
	}
	
	printf("%s\n", ans ? "YES" : "NO");
	
	return 0;
}