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