#include <iostream.h>

int main()
{
    long n, j, total;

    cout << "Enter number: ";
    cin >> n;


    total = 0;
    for (j = 1; j<=n; j++)
    {
        total += j;
    }
    cout << "The sum of the first " << n << " numbers is " << total << endl;

    cout << "Computed by the formula: " << n*(n+1)/2 << endl;
}