#include <bits/stdc++.h>
using namespace std;
char word[50];
int main()
{
    int col[45];
    col[1] = 1;
    for (int i = 2; i <= 39; i++)
    {
        col[i] = col[i - 1] + i - 1;
    }
    cout << col[39] + 20 - 1 << endl;
    return 0;
}