var f,g:text;
    p,n,m,s:longint;
begin
assign(f,'factorial.in');reset(f);
assign(g,'factorial.out');rewrite(g);
readln(f,m);
p:=5;
s:=-1;
n:=1;
while s<>m do
      begin
      s:=0;p:=5;
      while n div p<>0 do
            begin
            s:=s+n div p;
            p:=p*5;
            end;
      inc(n);
      end;
dec(n);
writeln(g,n);
close(f);
close(g);
end.