#include <bits/stdc++.h>
typedef long long ll;
using namespace std;

const int INF = 1e9;
const int MOD = 1e9+7;
const ll LINF = 1e18;

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) for(int i=0;i<(n);++i)
#define COUT(x) cout<<(x)<<"\n"

int main(){
    int a;
    cin >> a;
    vector<ll> vec;
    ll ans = 0;
    REP(i,a){
        ans += i;
        vec.push_back(ans);
        if(ans>=a)break;
    }
    bool flag = 0;
    REP(i,vec.size()){
        if(ans-vec[i]==a){
            flag = 1;
            break;
        }
        else if(ans<a)break;
    }
    if(flag)COUT("YES");
    else COUT("NO");
}