#include <stdio.h>

int N;
char S[5002];
short f[2][5001];

int main()
{
	scanf("%d%s", &N, S + 1);

	int i, j, current = 0;
	for (i = 1; i <= N; ++i){
		for (j = 1; j <= N; ++j){
			if (S[i] == S[N + 1 - j])
				f[current][j] = f[!current][j - 1] + 1;
			else if (f[current][j - 1] < f[!current][j])
					f[current][j] = f[!current][j];
			else f[current][j] = f[current][j - 1];

		}
		current = !current;
	}
	printf("%d", N - f[!current][N]);

	return 0;
}