#include <iostream>
using namespace std;
void selc(int n, int A[]){
    for(int i = 0; i < n; i++){
        int min = i;
        for(int j = i; j < n; j++){
            if(A[min] > A[j]) min = j;
        }
        int temp = A[i];
        A[i] = A[min];
        A[min] = temp;
    }
}
int main(){
    int n, x[100000];
    cin >> n;
    int flag = 0;
    for(int i = 0; i< n; i++) cin >> x[i];
    selc(n, x);
    for(int i = 0; i < n-2; i++){
        if(x[i+1] - x[i] == x[i+2] - x[i+1]) ;
        else flag = 1;
        if(x[i+1] == x[i]) flag = 1;
    }
    if(flag) cout << "NO" << endl;
    else cout << "YES" << endl;
    return 0;
}