Go: package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"strconv"
)

const (
	initialBufSize = 10000000
	maxBufSize     = 100000000
)

var sc *bufio.Scanner

func initScanner(r io.Reader) *bufio.Scanner {
	buf := make([]byte, initialBufSize)

	sc := bufio.NewScanner(r)
	sc.Buffer(buf, maxBufSize)
	sc.Split(bufio.ScanWords) // bufio.ScanLines
	return sc
}

func main() {
	sc = initScanner(os.Stdin)
	resolve()
}

func nextInt(sc *bufio.Scanner) int {
	sc.Scan()
	a, _ := strconv.Atoi(sc.Text())
	return int(a)
}
func nextString(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

func nextIntSlice(sc *bufio.Scanner, n int) (a []int) {
	a = make([]int, n)
	for i := 0; i < n; i++ {
		a[i] = nextInt(sc)
	}
	return a
}

var dp [][]int

func initDP(n int) {
	dp = make([][]int, n+1)
	for i := 0; i < len(dp); i++ {
		dp[i] = make([]int, n+1)
		for j := 0; j < len(dp[0]); j++ {
			dp[i][j] = -1
		}
	}
}

func resolve() {
	ans := []int{}
	for true {
		n := nextInt(sc)
		if n == 0 {
			break
		}
		as := nextIntSlice(sc, n)
		initDP(n)
		_rec(as, n, 0, n)
		ans = append(ans, dp[0][n])
	}
	for _, v := range ans {
		fmt.Println(v)
	}
	return
}

func _rec(as []int, n, l, r int) int {
	if dp[l][r] > -1 {
		return dp[l][r]
	}
	if r-l == 1 { // prevent to hit daruma
		dp[l][r] = 0
		return dp[l][r]
	}
	if r-l == 2 {
		if abs(as[l]-as[r-1]) <= 1 {
			dp[l][r] = 2
		} else {
			dp[l][r] = 0
		}
		return dp[l][r]
	}
	if abs(as[l]-as[r-1]) <= 1 {
		v := _rec(as, n, l+1, r-1)
		// if we can remove internal blocks
		if (r - 1 - (l + 1)) == v {
			dp[l][r] = v + 2
			return dp[l][r]
		} else {
			dp[l][r] = v
		}
	}
	for i := l + 1; i < r; i++ {
		v := _rec(as, n, l, i) + _rec(as, n, i, r)
		if dp[l][r] < v {
			dp[l][r] = v
		}
	}
	return dp[l][r]
}

func abs(v int) int {
	if v < 0 {
		return -v
	}
	return v
}

C++: #include <stdio.h>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
typedef long long int ll;
#define BIG_NUM 2000000000
#define MOD 1000000007
using namespace std;

bool** table;
int** dp;
int N;

int recursive(int left,int right){

	if(dp[left][right] != 0)return dp[left][right]; //?????¢???????????´???
	if(left == right)return 0;
	if((right-left+1)%2 == 1){ //??????????\???°?????´???
		return max(recursive(left,right-1),recursive(left+1,right));
	}
	if(table[left][(right-left+1)/2] == true)return dp[left][right] = right-left+1; //left???right?????¨????¶?????????´???
	if(right == left+1 && table[left][1] == false)return 0;

	int ans = 0;
	for(int i = left+1; i <= right-2; i++){
		ans = max(ans,recursive(left,i)+recursive(i+1,right));
	}
	return dp[left][right] = ans;
}

int main(){

	int data[301];
	table = new bool*[301]; //table[left][right] = left???????§?????????????2*right??????????????¨?¶??????§??????????????????
	dp = new int*[301]; //?????????????????????????????§?¶????????????°
	for(int i = 0; i <= 300; i++){
		table[i] = new bool[151];
		dp[i] = new int[151];
	}

	bool FLG;

	while(true){
		scanf("%d",&N);
		if(N == 0)break;

		if(N <= 1){
			printf("0\n");
			continue;
		}

		//?¶??????????????????????????????????
		for(int i = 0; i <= 300; i++){
			for(int k = 0; k <= 150; k++)table[i][k] = false;
			for(int k = 0; k <= 150; k++){
				dp[i][k] = 0;
			}
		}

		for(int i = 1; i <= N; i++)scanf("%d",&data[i]);

		//????????????2???????¨?
		for(int i = 1; i <= N-1; i++){
			if(abs(data[i+1]-data[i]) <= 1)table[i][1] = true;

		}

		//?¶??????????????????????????¨????
		for(int length = 4; length <= N; length += 2){ //??????????????????
			for(int left = 1; left+length -1 <= N; left++){ //??????????????????
				FLG = false;

				if(table[left+1][(length-2)/2] == true && abs(data[left] - data[left+length-1]) <= 1)FLG = true;//??????????????£?????????length-2??????????¶????????????????????????¨??????+length-1?????´???????????????????¶?????????´???

				if(!FLG){
					for(int i = 2; i <= length-2; i += 2){
						if(table[left][i/2] == true && table[left+i][(length-i)/2] == true){
							FLG = true;
							break;
						}
					}
				}
				if(FLG){
					table[left][length/2] = true;
				}
			}
		}

		printf("%d\n",recursive(1,N));
	}

	return 0;
}

C++: #include <bits/stdc++.h>
 
using namespace std;
using ll = long long;
 
#define rep(i, a) for (int i = 0; (i) < (int) (a); (i)++)
#define reps(i, a, b) for (int i = (int) (a); (i) < (int) (b); (i)++)
#define rrep(i, a) for (int i = (int) a-1; (i) >= 0; (i)--)
#define rreps(i, a, b) for (int i = (int) (a)-1; (i) >= (int) (b); (i)--)
#define MP(a, b) make_pair((a), (b))
#define PB(a) push_back((a))
#define all(v) (v).begin(), (v).end()
#define PERM(v) next_permutation(all(v))
#define UNIQUE(v) sort(all(v));(v).erase(unique(all(v)), v.end())
#define CIN(type, x) type x;cin >> x
#define TRUE__  "Yes"
#define FALSE__ "No"
#define PRINT(f) if((f)){cout << (TRUE__) << endl;}else{cout << FALSE__ << endl;}
#define RS resize
#define CINV(v, N) do {\
	v.RS(N);\
	rep(i, N) cin >> v[i];\
} while (0);
#define RCINV(v, N) do {\
	v.RS(N);\
	rrep(i, N) cin >> v[i];\
} while (0);
 
#define MOD 1000000007
bool init();
int solve();

signed main()
{
    while (init()) {
    	cout << solve() << endl;
	}
}

int N;
vector<int> w;

bool init()
{
	cin >> N;
	if (N == 0) return false;
	w.RS(N);
	rep(i, N) cin >> w[i];
	return true;
}


int solve()
{
	vector<vector<int> > dp;
	dp.RS(N, vector<int>(N, 0));
	rep(i, N) rep(j, N) dp[i][j] = abs(j - i) + 1;
	for (int i = 0; i + 1 < N; i++) {
		if (abs(w[i] - w[i+1]) <= 1) dp[i][i+1] = 0;
	}

	for (int l = 3; l <= N; l++) {
		for (int i = 0; i + l - 1 < N; i++) {
			int j = i + l - 1;
			int r = dp[i][j];
			reps(k, i, j) {
				r = min(r, dp[i][k] + dp[k+1][j]);
			}
			if (abs(w[i] - w[j]) <= 1 && dp[i+1][j-1] == 0) {
				r = 0;
			}
			dp[i][j] = r;
		}
	}
	return N - dp[0][N-1];
}