C :

int main(int argc, char* argv[])
{
	int a,b;
	while(~scanf("%d%d",&a,&b))
	{
	 printf("%.1lf\n",(5-3*b)*1.0/(2*a));
	}
	return 0;
}

C++ :

#include <iostream>
#include<iomanip>
using namespace std;

int main()
{
    int a,b;
    double x;
    cin>>a>>b;
    x=(5-3*b)*1.0/(2*a);
    cout<<fixed<<setprecision(1);
    cout<<x<<endl;
    return 0;
}