var f,g:text;
    nr,x,p,aux:longint;
begin
assign(f,'fact.in');reset(f);
assign(g,'fact.out');rewrite(g);
readln(f,p);
nr:=1;
x:=0;
while x<>p do
      begin
      nr:=nr+1;
      aux:=nr;
      while aux mod 5=0 do
            begin
            x:=x+1;
            aux:=aux div 5;
            end;
      end;
writeln(g,nr);
close(g);
end.