program infoarena_factorial;
var p,n,m,k,i,j,nrz:longint;


begin
assign(input,'fact.in');
reset(input);
readln(p);
close(input);

k:=p*5;

repeat
i:=5;
j:=trunc(k/i);
nrz:=0;

while j>0 do
begin
nrz:=nrz+j;
i:=i*5;
j:=trunc(k/i);
end;

k:=k-5;
until nrz<=p;

assign(output,'fact.out');
rewrite(output);
if nrz<p then writeln('-1')
 else if k=-5 then writeln('1')
  else writeln(k+5);
close(output);
end.