Program fact;
 var f,g:text; np,p:longint;
 procedure initiere;
  begin
   assign (f,'fact.in'); reset (f);
   assign (g,'fact.out'); rewrite (g);
   readln (f,p);
   np:=0;
  end;
 procedure incheiere;
  begin
   close (f); close (g);
  end;
 procedure taiere (var x:longint);
  var y:longint;
  begin
   while (x mod 10)=0 do begin
     x:=x div 10;
     np:=np+1;
   end;
   x:=x mod 10;
  end;
 procedure calcul;
  var x,y:longint;
  begin
   x:=1; y:=0;
   repeat
     y:=y+1;
     x:=x*y;
     taiere (x);
   until np=p;
   writeln (g,y);
  end;
 begin
  initiere;
  calcul;
  incheiere;
 end.