var a,b,c,tt,r,chuvi,dtich,option,dc1,dc2,dl,dn:real;
begin
writeln('1.Hinh tam giac');
writeln('2.Hinh tron');
writeln('3.Hinh thang');
write('Choose: ');readln(option);
if option = 1 then
        begin
        write('a = ');readln(a);
        write('b= ');readln(b);
        write('c = ');readln(c);
        if ((a+b)>c) and ((b+c)>a) and ((a+c)>b) then
                begin
                writeln('Chu vi tam giac la: ',a+b+c);
                chuvi:=(a+b+c)/2;
                dtich:=sqrt(chuvi*(chuvi-a)*(chuvi-b)*(chuvi-c));
                writeln('Dien tich tam giac la: ',dtich:2:2);
                tt:=sqrt(a*a/2-(b*b+c*c)/4);
                writeln('Do dai 1 duong trung tuyen la; ',tt:2:2);
                end
        else writeln('Error!');
        end;
if option = 2 then
        begin
        write('Ban kinh hinh tron: ');readln(r);
        writeln('Chu vi hinh tron: ',3.14*2*r:2:2);
        writeln('Dien tich hinh tron: ',3.14*r*r:2:2);
        end;
if option = 3 then
        begin
        dc1:=sqrt(6*6+3*3);
        dc2:=sqrt(3*3+3*3);
        chuvi:=19+dc1+dc2+10;
        dtich:=(10+19)*3/2;
        writeln('Chu vi hinh thang: ',chuvi:2:2);
        writeln('Dien tich hinh thang: ',dtich:2:2);
        end;
if (option <> 1) and (option <> 2) and (option <> 3) then write('Error!');
readln()
end.