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<bits/stdc++.h>
#define vi vector<int>
#define vvi vector<vector<int> >
template<typename Head, typename... Tail> auto vectors(Head x, Tail... tail) { auto inner = vectors(tail...); return vectors<decltype(inner)>(x, inner); }
using ll = long long;
using ld =long double;
#define int ll
#define INF 1e9
#define EPS 0.0000000001
#define rep(i,n) for(int i=0;i<n;i++)
#define loop(i,s,n) for(int i=s;i<n;i++)
#define all(in) in.begin(), in.end()
template<class T, class S> void cmin(T &a, const S &b) { if (a > b)a = b; }
template<class T, class S> void cmax(T &a, const S &b) { if (a < b)a = b; }
#define MAX 9999999
int dx[]={0,0,1,-1};
int dy[]={1,-1,0,0};
int W,H;
bool inrange(int x,int y){return (0<=x&&x<W)&&(0<=y&&y<H);}
using namespace std;
typedef pair<int, int> pii;
typedef pair<int,pii> piii;
#define MP make_pair
signed main(){
    int n;
    while(cin >> n,n){
        vector<vector<int>>dp(n,vector<int>(n,0));
        vector<int>array(n);
        rep(i,n) cin >> array[i];
        rep(k,n)rep(i,n-1){
            if(!k)continue;
            if(k == 1){
                if(abs(array[i]-array[i+1]) <= 1) dp[i][i+k] = 1;
            } else{
                if((abs(array[i]-array[i+k])<=1 && dp[i+1][i+k-1])){
                    cmax(dp[i][i+k],dp[i+1][i+k-1]+2);
                }
                for(int j = i+1; j<i+k && j<n-1;j++){
                    if(dp[i][j] && dp[j+1][i+k])cmax(dp[i][i+k],dp[i][j] + dp[j+1][i+k]);
                }
            }
        }
        int ans = 0;
        int maxi = 0;
        for(int i = maxi; i < n; i++){
            for(int j = n-1; j>=0;--j){
                if(dp[i][j]){
                    ans += j-i+1;
                    i = j;
                    break;
                }
            }
        }
        cout << ans << endl;
    }
}

C++: #include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <stack>
#include <queue>
#include <string>
#include <math.h>
#include <set>
  
#define REP(i,n)for (int i=0;i<(n);i++)
#define PB push_back
#define MP make_pair
#define ALL(a) (a).begin(),(a).end()
#define ll long long
using namespace std;
typedef pair<int,int> P;
int N, W[300], dp[300][300];
  
int rec(int l,int r){
	if(l>=r)return 0;
	if(dp[l][r]!=-1)return(dp[l][r]);
  	int ret = 0;
  	if(abs(W[l]-W[r])<=1&&rec(l+1,r-1)==r-l-1)ret=r-l+1;
  	for(int m=l;m<r;m++)ret=max(ret,rec(l,m)+rec(m+1,r));
  	return (dp[l][r]=ret);
}
  
int main(){
  	while(1){
		cin>>N;
    	for(int i=0;i<N;i++)cin>>W[i];
    	memset(dp,-1,sizeof(dp));
		cout<<rec(0,N-1)<<endl;
  	}
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

#define INF 1e9

int main(void){
  while(true){
    int n;
    cin >> n;
    if(n == 0){ break; }

    vector<int> w(n);
    for(int i = 0; i < n; i++){ cin >> w[i]; }

    vector<vector<int> > dp(n, vector<int>(n + 1, 0));
    for(int k = 2; k <= n; k++){
      for(int i = 0; i < n; i++){
        if(i + k <= n){
          for(int j = 1; j < k; j++)
            dp[i][i + k] = max(dp[i][i + k], dp[i][i + j] + dp[i + j][i + k]);
          if(dp[i + 1][i + k - 1] == k - 2 && abs(w[i] - w[i + k - 1]) <= 1)
            dp[i][i + k] = dp[i + 1][i + k - 1] + 2;
        }
      }
    }

    cout << dp[0][n] << endl;
  }

  return 0;
}

C++: #include <cmath>
#include <iostream>
#include <vector>
using namespace std;

int DFS(vector<int> &w, vector<bool> f, int n) {
  int max = 0;
  for (int i = 0; i < n; i++) {
    if (f[i]) {
      for (int j = i + 1; j < n; j++) {
	if (f[j]) {
	  if (abs(w[i] - w[j]) <= 1) {
	    f[i] = f[j] = false;
	    int ret = DFS(w, f, n) + 2;
	    f[i] = f[j] = true;
	    if (ret > max) {
	      max = ret;
	    }
	  }
	  break;
	}
      }
    }
  }
  return max;
}

int main() {
  vector<int> w(300);
  vector<bool> f(300);

  while (true) {
    int n;
    cin >> n;

    if (n == 0) {
      break;
    }

    for (int i = 0; i < n; i++) {
      cin >> w[i];
      f[i] = true;
    }

    cout << DFS(w, f, n) << endl;
  }

  return 0;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#define rep(i, n) for(int i = 0; i < (int)(n); ++i)
#define REP(i, n) for(int i = 1; i < (int)(n); ++i)
using namespace std;

vector<vector<int>> dp(400, vector<int>(400));
vector<int> a(400);

int rec(int l, int r) {
    if (abs(r - l) < 2) return 0;
    if (dp[l][r] != -1) return dp[l][r];
    
    int res = 0;
    if (abs(a[r - 1] - a[l]) < 2 && rec(l + 1, r - 1) == r - l - 2) res = r - l;
    for (int mid = l + 1; mid < r; ++mid) res = max(res, rec(l, mid) + rec(mid, r));
    dp[l][r] = res;
    return res;
}

int main() {
    while (true) {
        rep(i, 400) a[i] = 0;
        rep(i, 400) rep(j, 400) dp[i][j] = -1;
        int n;
        cin >> n;
        if (n == 0) break;
        rep(i, n) cin >> a[i];
        cout << rec(0, n) << endl;
    }
    return 0;
}