> #include<iostream>
> //#include<fstream>
> #define MAX 5002
> using namespace std;
> 
> int n,i,j,k;
> char pal[MAX],m[MAX][MAX];
> 
> int main()
> {
> 	//ifstream cin("input.txt");
> 	//ofstream cout("output.txt");
> 	while(cin >> n) {
> 		cin >> pal+1;
> 		for(i = 1;i <= n;i++) {
> 			for(j = n,k=1;j > 0;j--,k++) {
> 				if(pal[i] == pal[j])
> 					m[i][k] = m[i-1][k-1]+1;
> 				else if(m[i-1][k] > m[i][k-1])
> 					m[i][k] = m[i-1][k];
> 				else
> 					m[i][k] = m[i][k-1];
> 			}
> 		}
> 		cout << n-(int)m[n][n] << endl;
> 	}
> 	return 0;
> }