#include <bits/stdc++.h>
using namespace std;
double a,b,s;
int main()
{
cin>>a>>b;
s=a*b+a*a/2;
cout<<fixed<<setprecision(2)<<s;
return 0;
}
var a,b,s: real;
begin
write('Nhap a: '); readln(a);
write('Nhap b: '); readln(b);
s:=(((a*a)/2)+(a*b));
writeln(s:0:5);
end.