I don't know what is meant with the wording "at least four digits after decimal point". Does it mean the first four digits have to be exact ? I got WA with the format "%.4f" (at leat in Python) and i got AC with a code using the "%.5f" format. But the later doesn't guarantee you get the first four digits correct. For instance if x=10000085 then y=sqrt(x)=3162.291099819876... and "%.5f" %y prints 3162.29110 giving only 3 right digits after decimal point. And the examples given in the sample don't help.