10. Multiply by 2

#include <iostream>
#include<iomanip>

using namespace std;

int main() {
    double number;

    while (true) {
        cin >> number;

        if (number >= 0) {
            cout << "Result: " << fixed << setprecision(2) << number * 2 << endl;
        }
        else {
            cout << "Negative number!";
            break;
        }
    }

    return 0;
}