program factorial;
var p,n:longint;
    f:text;
function zerouri(x:longint):longint;
var cop, sum:longint;
begin
 cop:=x;
 sum:=0;
 while cop>0 do begin
  cop:=cop div 5;
  sum:=sum+cop;
 end;
 zerouri:=sum;
end;

procedure binar(a,b:longint);
var c,v:longint;
begin
 c:=(a+b)div 2;
 v:=zerouri(c);
 if (c=a)or(c=b)and(v<>p) then n:=-1 else
 if v<p then binar(c, b)
 else if v>p then binar(a,c)
 else n:=c-(c mod 5);
end;

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

        binar(1, maxlongint-1);

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