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 <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <utility>
#include <sstream>
#include <complex>
#include <fstream>
#include <bitset>
#include <time.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef complex<double> Point;

#define PI acos(-1.0)
#define EPS 1e-10
const ll INF = (1LL << 31) - 1;
const ll MOD = 1e9 + 7;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define rep(i,N) for(int i=0;i<(N);i++)
#define ALL(s) (s).begin(),(s).end()
#define EQ(a,b) (abs((a)-(b))<EPS)
#define EQV(a,b) ( EQ((a).real(), (b).real()) && EQ((a).imag(), (b).imag()) )
#define fi first
#define se second
#define N_SIZE (1LL << 20)
#define NIL -1
#define MAX_N 100100 * 3

int n;
int x[100];
int dp[300][300];
//int ans[300];

bool C(int lb, int ub) {
	//cout << lb << " " << ub /*<< dp[lb][ub]*/ << endl;
	if (dp[lb][ub] != -1)return dp[lb][ub];
	if (ub - lb <= 0)return dp[ub][lb] = 0;
	else if (ub - lb == 1) {
		if (abs(x[lb] - x[ub]) <= 1)return dp[lb][ub] = 1;
	}
	dp[lb][ub] = 0;
	if (abs(x[lb] - x[ub]) <= 1) {
		dp[lb][ub] |= C(lb + 1, ub - 1);
	}
	FOR(mid, lb, ub) {
		//cout << "!" << lb << " " << mid << endl;
		//cout << "!" << mid << " " << ub << endl;
		bool f = C(lb, mid);
		f &= C(mid + 1, ub);
		dp[lb][ub] |= f;
	}
	return dp[lb][ub];
}

int main() {
	while (cin >> n&&n) {
		rep(i, 300)rep(j, 300) {
			dp[i][j] = -1;
			//ans[i] = 0;
		}
		rep(i, n)cin >> x[i];
		C(0, n - 1);
		//rep(i, n) {
		//	FOR(j, i, n) {
		//		cout << i << " " << j << "  " << dp[i][j] << endl;
		//	}
		//}
		int ans = 0;
		rep(i, n) {
			//if (i >= 1)ans[i] = ans[i - 1];
			int num = 0;
			int pos = i;
			for (int j = i + 1; j < n; j += 2) {
				if (dp[i][j]) {
					num = max(num, j - i + 1);
					pos = j;
				}
			}
			ans += num;
			i = pos;
		}
		//rep(i, n) {
		//	FOR(j, i, n) {
		//		cout << i << " " << j << "  " << ans[i][j] << endl;
		//	}
		//}
		cout << ans << endl;
	}
}

C++: #include<bits/stdc++.h>
using namespace std;
#define INF 1e9

int main(){

    while(1){

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

        vector<vector<bool> > take(n, vector<bool> (n, false));        //take[i][j] := 区間[i][j]を全消しできるかどうか

        for(int k = 1; k < n; k++){
            for(int i = 0; i + k < n; i++){
                if(k == 1){
                    take[i][i + k] = (abs(w[i] - w[i + k]) <= 1);
                }else{
                    take[i][i + k] = (take[i + 1][i + k - 1] && abs(w[i] - w[i + k]) <= 1);
                
                    for(int l = i + 1; l < i + k; l++){
                        if(take[i][i + k]) break;
                        take[i][i + k] = (take[i][l] && take[l][i + k]);
                    }
                }
            }
        }

        vector<vector<int> > dp(n, vector<int> (n, 0));               //dp[i][j] := 区間 [i, j] において被覆できる頂点数の最大値

        //初期化
        for(int i = 0; i < n; i++){
            for(int j = i + 1; j < n; j++){
                if(take[i][j]) dp[i][j] = j - i + 1;
            }   
        }


        for(int k = 2; k < n; k++){
            for(int i = 0; i + k < n; i++){
                for(int l = i + 1; l < i + k; l++){
                    dp[i][i + k] = max(dp[i][i + k], dp[i][l] + dp[l + 1][i + k]);
                }  
            }
        }

        cout << dp[0][n - 1] << endl;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second
template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1 ; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1 ; } return 0; }
typedef long long ll;
typedef pair<int, int> pii;
const ll INF = 1e9+100;
const bool debug = 0;
/***************************************/

int N;
int a[300];
int dp1[300][301]; // [l, r]
int dp2[301];

int main() {
	while (cin >> N, N) {
		REP(i, N) scanf("%d", a + i);
		
		memset(dp1, 0, sizeof(dp1));
		REP(i, N - 1) if (abs(a[i] - a[i + 1]) <= 1) dp1[i][i + 1] = 2;
		FOR(w, 3, N + 1) {
			REP(i, N - w) {
				if (abs(a[i] - a[i+w]) > 1) continue;
				
				FOR(k, i + 2, i + w) {
					int l1 = i + 1, r1 = k - 1, l2 = k, r2 = i + w - 1;
					if (dp1[l1][r1] && dp1[l2][r2]) chmax(dp1[i][i+w], w + 1);
				}
				if (dp1[i+1][i+w-1]) chmax(dp1[i][i+w], w + 1);
			}
		}
		
		memset(dp2, 0, sizeof(dp2));
		REP(i, N) {
			FOR(j, i + 1, N) chmax(dp2[j + 1], dp2[i] + dp1[i][j]);
			chmax(dp2[i + 1], dp2[i]);
		}
		
		if (debug) printf("@ ");
		cout << dp2[N] << endl;
	}
	return 0;
}