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 || i+k>n-1)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<bits/stdc++.h>
using namespace std;
typedef pair<int, int> P;
const int M = 1000000007;

int main() {
    while (1) {
        int n;
        cin >> n;
        if (!n) return 0;

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

C++: #define _GLIBCXX_DEBUG

#include <bits/stdc++.h>


using namespace std;

#define DUMP(x) cout << #x << ": " << x << endl

int n;
int memo[310][310] = { false };
vector<int> w(n);

int rec(int l, int r) {
  if (r - l == 0) {
    return memo[l][r] = 2;
  }
  if (r - l == 1) {
    return memo[l][r] = 1;
  }
  
  if (r - l  - 1 == 1) {
    if (abs(w[r - 1] - w[l]) <= 1) {
      return memo[l][r] = 2;
    }
  }
  if (memo[l][r]) {
    return memo[l][r];
  }

  for (int t = l + 1; t < r; t++) {
    int temp  = rec(l, t);
    int temp2 = rec(t, r);
    int temp3 = rec(l + 1, t);
    int temp4 = rec(t, r - 1);
    
    if (temp == 2 && temp2 == 2) {
      return memo[l][r] = 2;
    }
    if (abs(w[l] - w[r - 1]) <= 1 && temp3 == 2 && temp4 == 2) {
      return memo[l][r] = 2;
    }
  }

  return memo[l][r] = 1;
}

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

    w.clear();
    w.resize(n);

    for (int i = 0; i < n; i++) {
      cin >> w[i];
    }
    memset(memo, 0, sizeof(memo));

    //    cerr << " " << rec(0, n) << endl;
    rec(0, n);
    int dp[310] = { 0 };
    dp[0] = 0;

    for (int r = 0; r <= n; r++) {
      dp[r] = dp[r - 1];
      for (int l = 0; l < r; l++) {
        if (memo[l][r] == 2) {
          dp[r] = max(dp[r], dp[l] + (r - l));
        }
      }
    }
    

    cout << dp[n] << endl;

  }

  

  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#include <string>
#include <cmath>
#include <algorithm>

using namespace std;

#define PB push_back
#define MP make_pair

typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> pii;
typedef vector<pii> vii;

const int MOD = 1e9+7;
const int INF = 1e9;

int main() {
  while (true) {
    int n, ans = 0;
    bool dp[300][300];
    cin >> n;
    if (n == 0) break;
    vi c;
    for (int i = 0; i < n; i++) {
      int tmp;
      cin >> tmp;
      c.PB(tmp);
    }
    for (int i = 0; i < 300; i++) {
      for (int j = 0; j < 300; j++) {
        dp[i][j] = false;
      }
    }
    for (int len = 2; len <= n; len+=2) {
      for (int left = 0; left+len <= n; left++) {
        int right = left + len - 1;
        if (abs(c[left]-c[right])<=1) {
          if (len==2) {
            dp[left][right] = true;
            // cout << len << ": " << left << "_a_" << right << endl;
            continue;
          } else {
            if (dp[left+1][right-1]) {
              dp[left][right] = true;
              // cout << len << ": " << left << "_b_" << right << endl;
              continue;
            }
          }
        }
        for (int pos = left+1; pos < right; pos+=2) {
          if (dp[left][pos] && dp[pos+1][right]) {
            dp[left][right] = true;
            // cout << len << ": " << left << "_c_" << right << endl;
            break;
          }
        }
      }
    }
    for (int left = 0; left < n; left++) {
      for (int right = n-1; left < right; right--) {
        if (dp[left][right]) {
          ans += right - left + 1;
          left = right + 1;
          break;
        }
      }
    }
    cout << ans << endl;
  }
  return 0;
}