575 B | 575 chars
#include <iostream>
using namespace std;
char a,b;
int main()
{
cin>>a;
if(a=='F') cout<<"0.0";
else
{
cin>>b;
switch(a)
{
case 'A':
if(b=='+') cout<<"4.3";
if(b=='0') cout<<"4.0";
if(b=='-') cout<<"3.7";
break;
case 'B':
if(b=='+') cout<<"3.3";
if(b=='0') cout<<"3.0";
if(b=='-') cout<<"2.7";
break;
case 'C':
if(b=='+') cout<<"2.3";
if(b=='0') cout<<"2.0";
if(b=='-') cout<<"1.7";
break;
case 'D':
if(b=='+') cout<<"1.3";
if(b=='0') cout<<"1.0";
if(b=='-') cout<<"0.7";
break;
}
}
}