#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("YES");}else{puts("NO");}
#define MAX_N 200005

int main() {
    int n;
    cin >> n;
    int x[n];
    rep(i,n)cin >> x[i];
    sort(x,x+n);

    int flag = 1;
    if(x[1] - x[0] == 0)flag = 0;
    int diff = x[1] - x[0];

    srep(i,1,n){
        if(x[i] - x[i-1] != diff)flag = 0;
    }

    if(flag)yn;
    
    return 0;
}