Program factorial;
VAR
  Be,Ki: Text;
  p,zero,n: Longint;

Function Nulla(x: Longint): Longint;
var szam: Longint;
Begin
szam:=0;
while x>=5 do begin
x:=x div 5;
inc(szam);
end;
Nulla:=szam;
end;

Function Binaris: Longint;
var i,lepes: Longint;
Begin
i:=0;
lepes:=1 shl 30;

while lepes <> 0 do begin
if Nulla(i+lepes) < p then i:=i+lepes;
lepes:=lepes div 2;
end;

if Nulla(i+1) > p then Binaris:=-1
else Binaris:= i+1;

end;


BEGIN

Assign(Be,'fact.in'); Reset(Be);
Assign(Ki,'fact.out'); Rewrite(Ki);

Read(Be,p);
Write(Ki,Binaris);
Close(Be); Close(Ki);

END.