Среднее из трёх

#include <iostream>
#include <vector>
#include <string>
#include <stdexcept>

double average_of_three(long long a, long long b, long long c) {
    // Calculate and return the average of three numbers
    return (a + b + c) / 3.0;
}

int main() {
    // Try your function with the first example. Change the input to test other cases.
    auto result = average_of_three(2, 4, 9);
    std::cout << result << std::endl;
    return 0;
}