#include <iostream>
#include <algorithm>
using namespace std;


int f(int x) {
    if(x == 5) {
        return 0;
    }

    return x + f(x + 1);

}
int main() {
    cout << f(1) << endl;

    return 0;
}

// f(1) = 1 + f(2) = 9 + 1 = 10
// f(2) = 2 + f(3) = 7 + 2 = 9
// f(3) = 3 + f(4) = 3 + 4 = 7
// f(4) = 4 + f(5) = 4 + 0 = 4
// f(5) = 0