#include <iostream>
using namespace std;

int main() {

    bool isIncorrect;
    int n;

    do {
        isIncorrect = false;

        cout << "Enter the value of n : ";
        cin >> n;

        if (cin.fail()) {
            cin.clear();
            cin.ignore();
            isIncorrect = true;
        }

        if (!isIncorrect && (n <= 0)) {
            isIncorrect = true;
        }

        if (isIncorrect) {
            cout << "Input Error. Check if the data is correct." << endl;
        }

        while (cin.get() != '\n');
    } while (isIncorrect);

    int sumOfNumbers = 0;
    int i;

    for (i = 1; i<=n; i++){
        sumOfNumbers += ((i-1)+i);
    }

    cout << "Sum of all numbers = " << sumOfNumbers;

    return 0;

}