E = mc² calculator, CC Lauri Friberg 2018, kilo, mega, gigaJ

//E = mc² calculator, CC Lauri Friberg 2018.
#include <iostream>
using namespace std;
int main()
{
double E=0, m=0, c=299792458;
cout << "E = mc², c=299 792 458 m/s, m = ?, E = ? J.\n";
cout << "m [kg] = ";
cin >> m;
E = m * c * c;
cout << "E = mc² = "<< m << " kg * " << c << "m²/s² = " << m << "kg * " << c*c << " m²/s² = " << m*c*c << " kgm²/s² = " << m*c*c << " J = " << E/1000 << " kJ "
    << " = " << E/100000 << " MJ = " <<  E/1000000000 << " GJ\n";
return 0;
}