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 <algorithm>
#include <vector>
#include <map>
#include <set>
#include <utility>
#include <tuple>
#include <math.h>
#include <iomanip>
#include <string>

using namespace std;

class Sover {
};

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

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

		vector<vector<bool>> can(n, vector<bool>(n, false));
		for (int i = 1; i < n; i += 2) {
			for (int j = 0; j + i < n; j++) {
				if (i == 1) {
					can[j][j + i] = abs(ws[j] - ws[j + i]) <= 1;
				}
				else {
					if (can[j + 1][j + i - 1]
						&& abs(ws[j] - ws[j + i]) <= 1)can[j][j + i] = true;
					else {
						for (int k = j + 1; k < j + i; k++) {
							if (can[j][k] && can[k + 1][j + i]) {
								can[j][j + i] = true;
								break;
							}
						}
					}
				}
			}
		}

		vector<int> dp(n, 0);
		for (int i = 0; i < n; i++) {
			if (i > 0)dp[i] = dp[i - 1];
			for (int j = 0; j < i; j++) {
				if (!can[j][i])continue;

				int tmp = i - j + 1;
				if (j > 0)tmp += dp[j - 1];
				dp[i] = max(dp[i], tmp);
			}
		}

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

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int (i)=(0);(i)<(int)(n);++(i))
using ll = long long;

int w[305], dp[305][305];

int main() {

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

        rep(i, n) cin >> w[i];
        rep(i, 305) rep(j, 305) dp[i][j] = 0;

        for (int ww=2; ww<=n; ++ww) {
            for (int i=0; i<n; ++i) {
                int j = i + ww - 1; // i - j ?????????
                if (j >= n) continue;

                if (dp[i+1][j-1] == ww-2 and abs(w[i] - w[j]) <= 1) dp[i][j] = ww;
                for (int k=i; k<j; ++k) {
                    dp[i][j] = max(dp[i][j], dp[i][k] + dp[k+1][j]);
                }
            }
        }

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

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[1000];
bool dp[1000][1000];

int main() {
	while (cin >> n&&n) {
		rep(i, 1000)rep(j, 1000) {
			dp[i][j] = 0;
		}
		rep(i, n)cin >> x[i];
		for (int i = 1; i < n; i += 2) {
			for (int j = 0; j + i < n; j++) {
				int lb = j, ub = j + i;
				if (abs(x[lb] - x[ub]) <= 1) {
					if (i == 1)dp[lb][ub] = 1;
					else dp[lb][ub] |= dp[lb + 1][ub - 1];
				}
				FOR(mid, lb, ub) {
					dp[lb][ub] |= dp[lb][mid] && dp[mid + 1][ub];
				}
			}
		}
		int ans = 0;
		rep(i, n) {
			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;
		}
		cout << ans << endl;
	}
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vs = vector<string>;
using msi = map<string, int>;
using mii = map<int, int>;
using psi = pair<string, int>;
using pii = pair<int, int>;
using vlai = valarray<int>;
#define rep(i,n) for(int i=0;i<n;i++)
#define range(i,s,n) for(int i=s;i<n;i++)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define fs first
#define sc second
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define INF (ll)1E9
#define EPS 1E-9
#define MOD 1000000007
#define PI 3.1415926535897932384

template <class T>ostream &operator<<(std::ostream &o, const vector<T> &v)
{
	rep(i, v.size()) {
		o << (i > 0 ? " " : "") << v[i];
	}
	return o;
}

//int dx[]={1,1,1,0,-1,-1,-1,0},dy[8]={1,0,-1,-1,-1,0,1,1,1};

//constexpr ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }

void solve(int n) {
	vi v(n, 0);
	vector<vector<bool>> dp(n + 1, vector<bool>(n, false));
	rep(i, n) {
		cin >> v[i];
	}
	for (int l = 2; l <= n; l += 2) {
		for (int i = 0; i + l <= n; i++) {
			bool b = false;
			if (l != 2) {
				for (int j = 2; j<l; j += 2) {
					if (dp[j][i] && dp[l - j][i + j])
						b = true;
				}
			}
			int dif = abs(v[i] - v[i + l - 1]);
			if (dif <= 1&&(l==2?1:dp[l-2][i+1]))b = true;
			if (b)dp[l][i] = true;
			//cout << l << " " << i << " " << dp[l][i] << endl;
		}
	}
	int pos = 0;
	queue<pii> q;
	q.push({ 0,0 });
	while (!q.empty()) {
		pii p = q.front(); q.pop();
		if (p.fs == n) {
			cout << n-p.sc << endl;
			return;
		}
		rep(i, n) {
			if (dp[i][p.fs])q.push({ p.fs+i,p.sc});
		}
		q.push({ p.fs+1 ,p.sc + 1 });
	}

}

int main(void) {
	int n;
	while (cin >> n, n) {
		solve(n);
	}
}