import std.stdio, std.string, std.conv, std.algorithm;
import std.range, std.array, std.math, std.typecons, std.functional;

void main() {
    int n = readln.chomp.to!int;
    auto x = readln.split.to!(int[]);

    x.sort();

    auto dif = x[1] - x[0];

    if (!dif) {
        writeln("NO");
        return;
    }

    bool check = iota(n - 1).all!(i => x[i + 1] - x[i] == dif);

    writeln(check ? "YES" : "NO");
}