var     p,nr,fac,x:int64;
        n,i,j:int64;
        f:text;
begin
assign(f,'fact.in');
reset(f);
read(f,p);
close(f);
nr:=0;
n:=1;
fac:=1;
while ((nr<p) and (n<10000000)) do
begin
inc(n);
fac:=fac*n;
x:=fac;
nr:=0;
while (x mod 10=0) do
begin
  inc(nr);
  x:=x div 10;
end;
end;


assign(f,'fact.out');
rewrite(f);
write(f,n);
close(f);
end.