var

x, y, a, d, dx, dy : real;

ulaz, izlaz : text;

begin

Assign(ulaz, ‘kvadrat.in’); Assign(izlaz, ‘kvadrat.out’);

Reset(ulaz); Rewrite(izlaz);

Read(ulaz, x, y, a);

x := abs(x); y := abs(y);

dx := 0; dy := 0;

if (x > a/2) then dx := x – a/2;

if (y > a/2) then dy := y – a/2;

d := sqrt(dx * dx + dy * dy);

WriteLn(izlaz, d);

Close(ulaz); Close(izlaz);

end.