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 <vector>
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<bits/stdc++.h>
using namespace std;
int dp[300][300];
int w[300];
int rec(int s,int t){
  if(dp[s][t]!=-1)return dp[s][t];
  if(s==t)return 0;
  int ans=rec(s+1,t-1);
  if(ans==t-s-1&&abs(w[s]-w[t])<=1)return dp[s][t]=ans+2;
  for(int i=s;i<t;i++){
    ans=max(ans,rec(s,i)+rec(i+1,t));
  }
  return dp[s][t]=ans;
}

int main(){
  int n;
  while(cin>>n,n){
    memset(w,0,sizeof(w));
    for(int i=0;i<n;i++)cin>>w[i];
    memset(dp,-1,sizeof(dp));
    for(int i=1;i<n;i++)
      dp[i-1][i]=(abs(w[i-1]-w[i])<=1?2:0);
    cout<<rec(0,n-1)<<endl;
  }
  return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define INF 1001000100010001000
#define MOD 1000000007
#define EPS 1e-10
#define int long long
#define rep(i, N) for (int i = 0; i < N; i++)
#define Rep(i, N) for (int i = 1; i < N; i++)
#define For(i, a, b) for (int i = (a); i < (b); i++)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define i_i pair<int, int>
#define vi vector<int>
#define vvi vector<vi >
#define vb vector<bool>
#define vvb vector<vb >
#define vp vector< i_i >
#define all(a) (a).begin(), (a).end()
#define Int(x) int x; cin >> x;
#define int2(x, y) Int(x); Int(y);
#define int3(x, y, z) Int(x); int2(y, z);
#define fir first
#define sec second
#define ffir first.first
#define fsec first.second
#define sfir second.first
#define ssec second.second
#define Decimal fixed << setprecision(10)

//int dxy[5] = {0, 1, 0, -1, 0}; 

int n;
int data[300];
int dp[300][301]; // hankai
int score[300][301];

void make(int st, int en)
{
    if (dp[st][en]) return;
    dp[st][en] = 1;
    if (0 <= st - 2 && abs(data[st-2] - data[st-1] ) < 2 ) {
        make(st-2, en);
    }
    if (0 <= st - 1 && en < n && abs(data[st-1] - data[en]) < 2) {
        make(st-1, en+1);
    }
    if (en + 1 < n && abs(data[en] - data[en+1]) < 2) {
        make(st, en+2);
    }
}

int solve(int st, int en)
{
    //cout << "call : " << st << " " << en << endl;;
    if ( dp[st][en] ) {
        //cout << " ret1 : 0" << endl;
        return score[st][en] = dp[st][en] = 0;
    }
    if ( score[st][en] ) {
        //cout << " ret2 : " << score[st][en] << endl;
        return score[st][en];
    }
    if (en - st < 2) {
        //cout << " ret3 : " << en - st << endl;
        return score[st][en] = en - st;
    }
    int ret = en - st;
    for (int i = st+2; i < en; i++) {
        if (dp[st][i]) {
            ret = min(solve(i, en), ret);
        }
    }
    return score[st][en] = min(ret, 1+solve(st+1, en));
    //score[st][en] = min(ret, 1+solve(st+1, en));
    //cout << score[st][en] << endl;
    //return score[st][en];
}

signed main() 
{ 
    std::ios::sync_with_stdio(false); 
    std::cin.tie(0); 

    cin >> n;
    while ( n ) {
        memset(data, 0, sizeof(data));
        memset(dp, 0, sizeof(dp));
        memset(score, 0, sizeof(score));
        rep(i, n) cin >> data[i];
        rep(i, n-1) if ( abs(data[i] - data[i+1]) < 2 )
            make(i, i+2);
        cout << n - solve(0, n) <<endl;
        cin >> n;
    }

    return 0; 
}