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OI-codes/Codeforces/47/A/A.cpp
2022-09-25 20:39:35 +08:00

18 lines
280 B
C++

#include <bits/stdc++.h>
using namespace std;
int main() {
int n;
cin >> n;
for (int i = 1; i <= n; i++) {
if ((i + 1) * i * 0.5 == n) {
cout << "YES" << endl;
goto end;
}
}
cout << "NO" << endl;
end:;
return 0;
}