#include using namespace std; #define SZ(x) (int) (x).size() #define REP(i, n) for(int i = 0; i < (n); i++) #define FOR(i, a, b) for(auto i = (a); i < (b); i++) #define For(i, a, b, c) \ for(auto i = (a); i != (b); i += (c)) #define REPR(i, n) for(auto i = (n) -1; i >= 0; i--) #define ALL(s) (s).begin(), (s).end() #define so(V) sort(ALL(V)) #define rev(V) reverse(ALL(V)) #define uni(v) v.erase(unique(ALL(v)), (v).end()) #define eb emplace_back typedef unsigned long long ull; typedef long long ll; typedef vector vi; typedef vector vll; typedef vector vb; typedef vector vvi; typedef vector vvll; typedef pair PI; typedef pair PL; const double EPS = 1e-6; const int MOD = 1e9 + 7; const int INF = (1 << 30); const ll LINF = 1e18; const double math_PI = acos(-1); template vector make_v(size_t a){ return vector(a); } template auto make_v(size_t a, Ts... ts){ return vector(ts...))>( a, make_v(ts...)); } template typename enable_if::value == 0>::type fill_v( T &t, const V &v){ t = v; } template typename enable_if::value != 0>::type fill_v( T &t, const V &v){ for(auto &e: t) fill_v(e, v); } template bool chmax(T &a, const T &b){ if(a < b){ a = b; return true; } return false; } template bool chmin(T &a, const T &b){ if(a > b){ a = b; return true; } return false; } template istream &operator>>(istream &is, pair &p){ cin >> p.first >> p.second; return is; } template istream &operator>>(istream &is, vector &vec){ for(T &x: vec) is >> x; return is; } template string join(vector &vec, string splitter){ stringstream ss; REP(i, SZ(vec)){ if(i != 0) ss << splitter; ss << vec[i]; } return ss.str(); } template ostream &operator<<(ostream &os, vector &vec){ os << join(vec, " "); return os; } int main(){ cin.tie(nullptr); ios::sync_with_stdio(false); int N; cin >> N; vi X(N); cin >> X; so(X); int diff = X[1] - X[0]; if(diff == 0){ cout << "NO" << endl; return 0; } REP(i, N - 1){ if(X[i + 1] - X[i] != diff){ cout << "NO" << endl; return 0; } } cout << "YES" << endl; return 0; }