func nextBlock(lastBlock Block) Block {

	blockIndex := lastBlock.index + 1
	blockTime := time.Now().String()
	blockData := "This is block " + strconv.Itoa(blockIndex)
	previousHash := lastBlock.previousHash

	var sha = sha256.New()
	tryString := lastBlock.previousHash
	rand.Seed(time.Now().UnixNano())
	nonce := make([]byte, 4)
	rand.Read(nonce)

	hashString := "00000" + lastBlock.previousHash[5:len(lastBlock.previousHash)]

	for ((tryString[:5]) != hashString[:5]) {


			sha.Write([]byte(tryString))
			tryString = hex.EncodeToString(sha.Sum(nil))
			tryString = tryString + hex.EncodeToString(nonce)
			fmt.Printf(tryString)
			fmt.Printf("\n\n")

			nonce[3]++
	}

 	blockString := strconv.Itoa(blockIndex) + blockTime + blockData + previousHash + tryString
	var sha2 = sha256.New()
	sha2.Write([]byte(blockString))

	t, err := os.Create("height")
	check(err)
	n, err := t.WriteString(strconv.Itoa(blockIndex))
	fmt.Printf("Written height to file", n)
	t.Sync()

	return Block {blockIndex, time.Now(), blockData, hex.EncodeToString(sha2.Sum(nil)) }

}