#include <bits/stdc++.h>

using namespace std;
#define N 55
int a[N];

int main() {
    a[1] = 0;
    for (int i = 2; i <= 50; ++i)
        a[i] = a[i - 1] + (i - 1);
    cout << (a[50] - a[7]) << endl;
    return 0;
}