#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>

using namespace std;

int main()
{
    int sum=0;
    int day;
    cin>>day;
    for(int i=0;i<5000;i++){
        for(int j=0;j<=i;j++){
            sum+=i+1;
            day--;
            if(day==0) {cout<<sum; return 0;}
        }
    }
    return 0;
}