#include <iostream> using namespace std; int main() { int days; cin >> days; int total_coins = 0; int current_day = 1; int coins_per_day = 1; int days_in_period = 1; while (current_day <= days) { for (int i = 0; i < days_in_period && current_day <= days; i++) { total_coins += coins_per_day; current_day++; } coins_per_day++; days_in_period++; } cout << total_coins << endl; return 0; }