#include <bits/stdc++.h>
using namespace std;
int n,m;
string s;
vector<char> a;
int main()
{
    cin >> n >> s;
    for (auto i:s)
        if (a.empty() || a.back() != i)
            a.push_back(i);
    m = a.size();
    vector<vector<int> > dp(m+1,vector<int>(m+1,0));
    for (int i=0;i<m;i++)
        dp[i][i] = 1;
    for (int len=2;len<=m;len++)
    for (int l=0;l+len-1<m;l++)
    {
        int r = l + len - 1;
        dp[l][r] = dp[l+1][r] + 1;
        for (int k=l+1;k<=r;k++)
            if (a[l] == a[k])
                dp[l][r] = min(dp[l][r],dp[l+1][k-1]+dp[k][r]);
    }
    cout << dp[0][m-1];
    return 0;
}