C++ :: Operator Overloading - Comparing Objects (Fractions)

I'm trying to compare 2 fractions using operator overloading. The program crashes when this is called;

this is definition:
bool operator == (const Fraction& f1, Fraction& f2) {
if (f1==f2)return true;
else return false;
}

this is my calling in the main:
Fraction f1, f2;
cout<<"Enter in the format: 2/4 or 4/9
";
cout << "enter first fraction: ";
f1.Input();
cout << "enter second fraction: ";
f2.Input();

Fraction result:
result = (f1 == f2);//i think problem lies here.
result.Show();

and this is the prototype of the operator:
friend bool operator == (const Fraction& f1, Fraction& f2);