program ural1283;
const
  zero=1e-6;
var
  a,b:longint;
  c:real;
begin
  read(a,b,c);
  writeln(trunc(ln(b/a)/ln(1-c/100)+1+zero));
end.

My old formula was wrong, and a new one is here in the prog below.

When I submit, I comment out either part. But neither simulation nor formula works, they both get WA #1.

BTW, what is the output for 2 1 50? Is it 1 or 2?

program ural1283;
var
  b,ans:longint;
  a,c:real;
begin
  read(a,b,c);
  c:=1-c/100;
//Simulation:
  while a>=b do begin
    inc(ans);
    a:=a*c;
  end;
  writeln(ans);
//Formula:
  ans:=trunc(ln(b/a)/ln(c)+1);
  if ans<0 then writeln(0) else writeln(ans);
end.