var  f,g:text;
     sem:boolean;
     p,nr,d,x:longint;
function factorial(x:longint):longint;
begin
     if x=0 then
        factorial:=1
     else
         factorial:=x*factorial(x-1);
end;
begin
     assign(f,'fact.in');
     reset(f);
     assign(g,'fact.out');
     rewrite(g);
     readln(f,p);
     nr:=1;
     sem:=false;
     if p=0 then
     begin
        write(g,nr);
        nr:=p div 2+ (4*p)
     end
     else
     while sem=false do
           begin
                inc(nr);
                x:=factorial(nr);
                d:=0;
                while x mod 10 =0 do
                      begin
                           inc(d);
                           x:=x div 10;
                      end;
                if d=p then
                begin
                   write(g,nr);
                   sem:=true;
                end;
           end;
     close(f);
     close(g);
readln;
end.