uses crt;
var a,b,h,s:real
begin
clrscr;
write('A B H -> ');
readln(a,b,h);
s:=h*(a+b)/2;
writeln('S=',s:0:4);
readln;
end.
uses crt;
var a,b,h,s:real
begin
clrscr;
write('A B H -> ');
readln(a,b,h);
s:=h*(a+b)/2;
writeln('S=',s:0:4);
readln;
end.