#include <cstdio>
#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <typeinfo>
#include <numeric>
#include <functional>
#include <unordered_map>
#include <bitset>
#include <stack>
#include <assert.h>
#include <unordered_set>
#include <random>
// #include <atcoder/all>


using namespace std;
// using namespace atcoder;
using ll = long long;
using ull = unsigned long long;

const ll INF = 1e18;
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;


#define REP(i, n) for(ll i = 0; i < n; i++)



















int main(){
    ll a;
    cin >> a;
    ll r = 1, s = 0;
    for(ll l = 1; l <= 1e9 / 2.5; l++){
        while(s < a){
            s += r++;
        }
        if(s == a){
            cout << "YES" << endl;
            return 0;
        }
    }
    cout << "NO" << endl;
}