大数乘c++

#include<iostream>
using namespace std;
int cheng(int x,int y)
{
	int sum;
	sum=x*y;
	return sum;
	
}
double cheng(double x,double y)
{
	double sum;
	sum=x*y;
	return sum;
	
}
int main()
{
	double x,y;
	cin>>x>>y;
	if(x==(int)x && y==(int)y)
		cout<<cheng((int)x,(int)y);
	else
		cout<<cheng(x,y);

}