// lanqiao 1457 杨辉三角形(朴素解法)
#include<bits/stdc++.h>
using namespace std;
#define int long long 
const int N = 1e3 + 10;
int a[N][N];
signed main(){
    int n; cin >>n;
    if(n == 1){
        cout << 1 << endl;
        return 0;
    } 
    a[1][1] = a[2][1] = a[2][2] = 1;
    for(int i = 3; i <= N-1; i++){
        for(int j = 1; j <= i; j++){
            if(j == 1 || j == i) a[i][j] = 1;
            else a[i][j] = a[i-1][j] + a[i-1][j-1];
            if(a[i][j] == n){ // 1 + 2 + ... + i-1
                cout << i*(i-1)/2 + j << endl;
                return 0;
            }
        }
    }
    return 0;
}
/* test samples -> 13
6
*/