#include <iostream>
#include <cmath>

double suma(double a, double q, size_t n) {
    return a * (1. - std::pow(q, n)) / (1. - q);
}

int main() {
    double a, q;

    std::cout << "a(n) = a * q^(n - 1)" << std::endl;
    std::cout << "S(n) = suma n wyrazów ciągu a" << std::endl;
    std::cout << "a = ";
    std::cin >> a;

    std::cout << "q = ";
    std::cin >> q;

    while(true) {
        size_t n;
        std::cout << "n = ";
        std::cin >> n;

        std::cout << "a(n) = " << (a * std::pow(q, n - 1)) << std::endl;
        std::cout << "S(n) = " << suma(a, q, n) << std::endl << std::endl;
    }

    return 0;
}