#include <bits/stdc++.h>
#define ll long long 

using namespace std;

const int N = 2005;

ll f[N][N];

int main()
{
    int n;
    cin >> n;

    for (int i = 1; i < N; i ++ )
        for (int j = 1; j <= i; j ++ )
        {
            if (i == 1 && j == 1) f[i][j] = 1;
            else f[i][j] = f[i - 1][j] + f[i - 1][j - 1];
            if (f[i][j] > 1e9) f[i][j] = 1e10;
            if (f[i][j] == n)
            {
                cout << i * 1ll * (i - 1) / 2 + j << endl;
                return 0;
            }
        }

    int m = sqrt(n * 2) + 1;
    if (m * (m - 1) / 2 == 0) cout << m * 1ll * (m + 1) / 2 + 3 << endl;
    else cout << n * 1ll * (n + 1) / 2 + 2 << endl;

    return 0;
}