www.pudn.com > TJU.rar > ac1077.pas

program tju1077; 
var 
  a,b,i,j:word; 
  lnc,lnd,ans:extended; 
begin 
  repeat 
    read(b,a,i,j); 
    a:=(a-1) div i+1;b:=(b-1) div j+1; 
    lnc:=0;lnd:=ln(2)*(a+b-1);ans:=0; 
    for i:=a+b-1 downto a do begin 
      ans:=ans+exp(lnc-lnd); 
      lnc:=lnc-ln(a+b-i)+ln(i); 
    end; 
    writeln(ans*100:0:4); 
  until seekeof; 
end.