#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <string>
#include <math.h>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <stdio.h>
#include <numeric>
#include <iomanip>
#include <random>
using namespace std;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
long long n;
cin >> n;
long long l = 0, r = 1e18;
while (l + 1 < r) {
long long m = (l + r) / 2;
if ((long double) m > (long double) 2e18 / (m + 1) || m * (m + 1) / 2 > n) {
r = m;
} else {
l = m;
}
}
if (l * (l + 1) / 2 == n) cout << l * l;
else {
cout << l * l + (n - l * (l + 1) / 2) * 2 - 1;
}
return 0;
}
