#include <bits/stdc++.h>

template<typename T> T in() { abort(); return T(); }
template<> std::string in() { std::string str; std::cin >> str; return str; }
template<> int in() { int x; scanf("%d", &x); return x; }

template<typename T> void out(T x) { abort(); }
template<> void out(const char* x) { printf("%s\n", x); }
template<> void out(std::string x) { std::cout << x << std::endl; }
template<> void out(int x) { printf("%d\n", x); }

int n;
int xs[112345];

int main() {
  n = in<int>();
  for(int i = 0; i < n; ++i) {
    xs[i] = in<int>();
  }
  std::sort(xs, xs + n);
  int d = xs[1] - xs[0];
  bool flag = d == 0 ? false : true;
  for(int i = 1; i < n; ++i) {
    if( xs[i] - xs[i - 1] != d ) {
      flag = false;
      break;
    }
  }
  out(flag ? "YES" : "NO");
  
  
  return 0;
}