var n:longint;
    x5:longint;
    i:integer;

function power(x:integer):integer;
 var rez:integer;
begin
 rez:=0;
 while x mod 5 = 0 do
  begin
   inc(rez);
   x:=x div 5;
  end;
 power:=rez;
end;

begin
 //assign(input,'fact.in');
 //reset(input);
 readln(n);
 x5:=0;
 i:=1;
 while x5<n do
 begin
  inc(x5,power(i));
  inc(i);	
 end;
 if i=1 then writeln('1') else if (i-1) mod 10 = 0 then writeln(i-1) else writeln('-1');
end.