var  p,c,n,p2,m:longint  ;f,g:text;
function nr0(n:longint):longint;
var x,p2:longint;
begin
     x:=5; p2:=0;
     while n>=x do begin
           p2:=p2+n div x;
           x:=x*5;
     end;
     nr0:=p2
end;

begin
     assign(f,'fact.in'); reset(f);
     assign(g,'fact.out');rewrite(g);
     read(f,p);
     c:=1;
     n:=200000000;
     repeat
          m:=(n+c) div 2;
          p2:=nr0(m);
          if (p2>p) then n:=m
          else if p2<p then c:=m
     until (p2=p)or(n-c<=1);
     p2:=nr0((n+c) div 2);
     if p2<>p then write(g,-1)
     else begin
     while nr0(m-1)=p do
           m:=m-1;
     writeln(g,m);
     end;
     close(g);
end.