C :

#include<stdio.h>

int main(int argc , char** argv)
{
	double s,h,a,b;
	scanf ("%lf%lf%lf",&h,&a,&b);
	s=(a+b)*h/2.0;
	printf ("%.2f" , s);
	return 0;
}

C++ :

#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
	float s,h,a,b;
	cin>>h>>a>>b;
	s=h*(a+b)/2;
	printf("%.2f",s);
	return 0;
}

Pascal :

program xx;
var h,a,b:integer;
    s:real;
begin
readln(h);
readln(a,b);
s:=1/2*h*(a+b);
writeln(s:3:2);
end.