i += len(old)
					n--
					if len(old) != 0 {
						continue
					}
					if i == len(in) {
						break
					}
				}
				if len(old) == 0 {
					_, length := utf8.DecodeRune(in[i:])
					out.Write(in[i : i+length])
					i += length
				} else {
					out.WriteByte(in[i])
					i++
				}
			}
			if len(old) == 0 && n != 0 {
				out.Write(new)
			}