You are given a string s of length n consisting of lowercase Latin letters. You may apply some operations to this string: in one operation you can delete some contiguous substring of this string, if all letters in the substring you delete are equal. For example, after deleting substring bbbb from string abbbbaccdd we get the string aaccdd.

Calculate the minimum number of operations to delete the whole string s.

Input

The first line contains one integer n (1 ≤ n ≤ 500) — the length of string s.

The second line contains the string s (|s| = n) consisting of lowercase Latin letters.

Output

Output a single integer — the minimal number of operation to delete string s.

Examples

Input


5
abaca


Output


3

Input


8
abcddcba


Output


4
 /*                       In_The_Name_Of_Allah_The_Merciful                        */
import java.util.*;
import java.io.*;  
public class Main 
{
    PrintWriter out;
    FastReader sc;
    long[] m1= {(long)(1e9+7),998244353};
    long mod=m1[0];
    long maxlong=Long.MAX_VALUE;
    long minlong=Long.MIN_VALUE;
    StringBuilder sb;

    /******************************************************************************************
     *****************************************************************************************/
   
	public void sol(){
		int n=ni();
		char[] s=rl();
		long[][] dp=new long[n][n];
		for(int i=0;i<n;i++) {
			for(int j=0;j<n;j++) {
				dp[i][j]=maxlong;
				if (i > j)
 					dp[i][j] = 0;
			}
		}for(int i=0;i<n;i++)dp[i][i]=1;
		for(int i=1;i<n;i++) {
			for(int j=0;j+i<n;j++) {
				dp[j][j+i]=min(dp[j][j+i],1+dp[j+1][j+i]);
				for(int k=j+1;k<=j+i;k++) {
					if(s[j]==s[k])
					dp[j][j+i]=min(dp[j][j+i],dp[j+1][k-1]+dp[k][j+i]);
				}
			}
		}pl(dp[0][n-1]);
	}
    public static void main(String[] args) 
	{ 
	    Main g=new Main();
		g.out=new PrintWriter(System.out);
		g.sc=new FastReader();
		int t=1;
// 		t=g.ni();
		while(t-->0)
		g.sol();
		g.out.flush();
	}
	
	/****************************************************************************************
     *****************************************************************************************/
	static class FastReader 
	{ 
		BufferedReader br; 
		StringTokenizer st; 
 
		public FastReader() 
		{ 
			br = new BufferedReader(new
					InputStreamReader(System.in)); 
		} 
 
		String next() 
		{ 
			while (st == null || !st.hasMoreElements()) 
			{ 
				try
				{ 
					st = new StringTokenizer(br.readLine()); 
				} 
				catch (IOException e) 
				{ 
					e.printStackTrace(); 
				} 
			} 
			return st.nextToken(); 
		} 
 
		int nextInt() 
		{ 
			return Integer.parseInt(next()); 
		} 
 
		long nextLong() 
		{ 
			return Long.parseLong(next()); 
		} 
 
		double nextDouble() 
		{ 
			return Double.parseDouble(next()); 
		} 
 
		String nextLine() 
		{ 
			String str = ""; 
			try
			{ 
				str = br.readLine(); 
			} 
			catch (IOException e) 
			{ 
				e.printStackTrace(); 
			} 
			return str; 
		} 
	} public int ni(){
	      return sc.nextInt();
	}public long nl(){
	      return sc.nextLong();
	}public double nd(){
	      return sc.nextDouble();
	}public char[] rl(){
	      return sc.nextLine().toCharArray();
	}public String rl1(){
	      return sc.nextLine();
	}
	public void pl(Object s){
	      out.println(s);
	}
	public void pr(Object s){
	      out.print(s);
	}public String next(){
	      return sc.next();
	}public long abs(long x){
	      return Math.abs(x);
	}
	public int abs(int x){
	      return Math.abs(x);
	}
	public double abs(double x){
	      return Math.abs(x);
	}public long min(long x,long y){
            return (long)Math.min(x,y);
      }
      public int min(int x,int y){
            return (int)Math.min(x,y);
      }
      public double min(double x,double y){
            return Math.min(x,y);
      }public long gcd(long a, long b) {
		if (a == 0)
			return b;
		return gcd(b % a, a);
	}public long lcm(long a, long b) {
            return (a / gcd(a, b)) * b;
      }
       void sort1(int[] a) {
		ArrayList<Integer> l = new ArrayList<>();
		for (int i : a) {
			l.add(i);
		}
		Collections.sort(l,Collections.reverseOrder());
		for (int i = 0; i < a.length; i++) {
			a[i] = l.get(i);
		}
	}
	 void sort(int[] a) {
		ArrayList<Integer> l = new ArrayList<>();
		for (int i : a) {
			l.add(i);
		}
		Collections.sort(l);
		for (int i = 0; i < a.length; i++) {
			a[i] = l.get(i);
		}
	}void sort(char[] a) {
		ArrayList<Character> l = new ArrayList<>();
		for (char i : a) {
			l.add(i);
		}
		Collections.sort(l);
		for (int i = 0; i < a.length; i++) {
			a[i] = l.get(i);
		}
	}void sort1(char[] a) {
		ArrayList<Character> l = new ArrayList<>();
		for (char i : a) {
			l.add(i);
		}
		Collections.sort(l,Collections.reverseOrder());
		for (int i = 0; i < a.length; i++) {
			a[i] = l.get(i);
		}
	}
	 void sort(long[] a) {
		ArrayList<Long> l = new ArrayList<>();
		for (long i : a) {
			l.add(i);
		}
		Collections.sort(l);
		for (int i = 0; i < a.length; i++) {
			a[i] = l.get(i);
		}
	}void sort1(long[] a) {
		ArrayList<Long> l = new ArrayList<>();
		for (long i : a) {
			l.add(i);
		}
		Collections.sort(l,Collections.reverseOrder());
		for (int i = 0; i < a.length; i++) {
			a[i] = l.get(i);
		}
	}
	void sort(double[] a) {
		ArrayList<Double> l = new ArrayList<>();
		for (double i : a) {
			l.add(i);
		}
		Collections.sort(l);
		for (int i = 0; i < a.length; i++) {
			a[i] = l.get(i);
		}
	}long pow(long a,long b){
          if(b==0){
                return 1;
          }long p=pow(a,b/2);
          if(b%2==0) return mMultiplication(p,p)%mod;
          else return (mMultiplication(mMultiplication(p,p),a))%mod;
    }
	
	int  swap(int a,int b){
	      return a;
	}long  swap(long a,long b){
	      return a;
	}double  swap(double a,double b){
	      return a;
	}
	boolean isPowerOfTwo (int x) 
      { 
            return x!=0 && ((x&(x-1)) == 0);     
      }boolean isPowerOfTwo (long x) 
      { 
            return x!=0 && ((x&(x-1)) == 0);     
      }public long max(long x,long y){
            return (long)Math.max(x,y);
      }
      public int max(int x,int y){
            return (int)Math.max(x,y);
      }
      public double max(double x,double y){
            return Math.max(x,y);
      }long sqrt(long x){
            return (long)Math.sqrt(x);
      }int sqrt(int x){
            return (int)Math.sqrt(x);
      }void input(int[] ar,int n){
            for(int i=0;i<n;i++)ar[i]=ni();
      }void input(long[] ar,int n){
            for(int i=0;i<n;i++)ar[i]=nl();
      }void fill(int[] ar,int k){
            Arrays.fill(ar,k);
      }void yes(){
            pl("YES");
      }void no(){
            pl("NO");
      }
      long c2(long n) {
    	  return (n*(n-1))/2;
      }
    long[] sieve(int n) 
    {
          long[] k=new long[n+1];
          boolean[] pr=new boolean[n+1];
          for(int i=1;i<=n;i++){
                k[i]=i;
                pr[i]=true;
          }for(int i=2;i<=n;i++){
                if(pr[i]){
                      for(int j=i+i;j<=n;j+=i){
                            pr[j]=false;
                            if(k[j]==j){
                                  k[j]=i;
                            }
                      }
                }
          }return k;
    }
    int strSmall(int[] arr, int target)  
    {  
        int start = 0, end = arr.length-1;  
        int ans = -1;  
        while (start <= end) {  
            int mid = (start + end) / 2;   
            if (arr[mid] >= target) {  
                end = mid - 1;  
            }   
            else {  
                ans = mid;  
                start = mid + 1;  
            }  
        }  
        return ans;  
    } int strSmall(ArrayList<Integer> arr, int target)  
    {  
        int start = 0, end = arr.size()-1;  
        int ans = -1;  
        while (start <= end) {  
            int mid = (start + end) / 2;   
            if (arr.get(mid) > target) {  
                start = mid + 1; 
                ans=start;
            }   
            else {
                end = mid - 1;  
            }  
        }  
        return ans;  
    }long mMultiplication(long a,long b) 
    { 
        long res = 0;    
        a %= mod; 
  
        while (b > 0)  
        {  
            if ((b & 1) > 0)  
            { 
                res = (res + a) % mod; 
            }  
            a = (2 * a) % mod; 
  
            b >>= 1;  
        } 
        return res; 
    }long nCr(int n, int r ,long p)
    {
 
          if (n<r) 
              return 0;
        if (r == 0)
            return 1;
            long[] fac = new long[n + 1];
        fac[0] = 1;
 
        for (int i = 1; i <= n; i++)
            fac[i] = fac[i - 1] * i %p;
        return (fac[n] * modInverse(fac[r], p)
                % p * modInverse(fac[n - r], p)
                % p)
            % p;
    }long power(long x, long y, long p)
    {
        long res = 1;
        x = x % p;
 
        while (y > 0) {
            if (y % 2 == 1)
                res = (res * x) % p;
            y = y >> 1; 
            x = (x * x) % p;
        }
 
        return res;
    }long modInverse(long n, long p)
    {
        return power(n, p - 2, p);
    }
    
    int[][] floydWarshall(int graph[][],int INF,int V)
    {
        int dist[][] = new int[V][V];
        int i, j, k;
        for (i = 0; i < V; i++)
            for (j = 0; j < V; j++)
                dist[i][j] = graph[i][j];
        for (k = 0; k < V; k++)
        {
            for (i = 0; i < V; i++)
            {
                for (j = 0; j < V; j++)
                {
                    if (dist[i][k] + dist[k][j] < dist[i][j])
                        dist[i][j] = dist[i][k] + dist[k][j];
                }
            }
        }return dist;
    }
    class minque {
		Deque<Long> q;
		minque(){
			q=new ArrayDeque<Long>();
		}public void add(long p){
			while(!q.isEmpty()&&q.peekLast()>p)q.pollLast();
			q.addLast(p);
		}public void remove(long p) {
			if(!q.isEmpty()&&q.getFirst()==p)q.removeFirst();
		}public long min() {
			return q.getFirst();
		}
	}
      int find(subset[] subsets, int i)
      {
          if (subsets[i].parent != i)
              subsets[i].parent
                  = find(subsets, subsets[i].parent);
          return subsets[i].parent;
      }void Union(subset[] subsets, int x, int y)
      {
          int xroot = find(subsets, x);
          int yroot = find(subsets, y);
   
          if (subsets[xroot].rank < subsets[yroot].rank) {
          	subsets[xroot].parent = yroot;
          }
          else if (subsets[yroot].rank < subsets[xroot].rank) {
          	subsets[yroot].parent = xroot;
          }
          else {
              subsets[xroot].parent = yroot;
              subsets[yroot].rank++;
          }
      }class subset
      {
          int parent;
          int rank;
      }
	 
} 