#include<iostream>
using namespace std;
long long int f[100][100], n, s;
int main()
{
	cin >> n;
	for (int i = 0; i <= 99; i++)
		f[i][0] = 1;
	if (n == 1)
	{
		cout << 1;
		return 0;
	}
	for (int i = 1; i <= 99; i++)
	{
		for (int j = 1; j <= i; j++)
		{
			f[i][j] = f[i - 1][j] + f[i - 1][j - 1];
			if (f[i][j] == n)
			{
				s = i * (i + 1) / 2 + j + 1;
				cout << s;
				return 0;
			}
		}
	}
	return 0;
}