program factorial;
var f1,f2:text; p,n,x,c,y:longint;
begin
assign(f1,'fact.in');
reset(f1);
read(f1,p);
n:=0;
x:=0;
c:=0;
repeat
x:=x+1;
y:=x;
if (y mod 5=0) then
   repeat
   y:=y div 5;
   c:=c+1
   until (y=0) or (y mod 5<>0);
n:=n+1
until (c=p) or (c>p);
if c>p then
n:=-1;
assign(f2,'fact.out');
rewrite(f2);
writeln(n);
end.