Submission #1778745

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Source Code Expand

#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define ALL(A) A.begin(), A.end()

using namespace std;

typedef long long ll;
typedef pair<int, int> P;

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	ll X; cin >> X;

	ll res = X;
	ll low = 0LL;
	ll high = X;

	int iter = 0;
	while(low < high && iter < 30){
		ll mid = (low + high) / 2LL;
		if (mid * (mid + 1LL) / 2LL < X){
			low = mid;
		}else{
			res = min(res, mid);
			high = mid;
		} // end if
		++iter;
	} // end while

	cout << res << endl; 
	
	return 0;
}

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