func growSlice(b []byte) []byte {
	newCap := 10
	if cap(b) > 5 {
		newCap = cap(b) * 2
	}
	b1 := make([]byte, len(b), newCap)
	copy(b1, b)
	return b1
}
func X(b []byte) []byte {
if len(b) == cap(b) {
b = growSlice(b)
}
b = b[:len(b)+1]
b[len(b)-1] = 3
return b
}
package stackmap
func X(b []byte) []byte