hdu 1513

#include<stdio.h>
#include<string.h> 
#include<iostream>
#include<math.h>
using namespace std;

char s1[5005],s2[5005];
int dp[2][5005],n;

void lcs()
{
    int i,j;
    memset(dp,0,sizeof(dp));
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=n;j++)
        {
            int x=i%2;
            int y=1-x;
            if(s1[i-1] == s2[j-1])
                dp[x][j]=dp[y][j-1]+1;
            else
                dp[x][j]=max(dp[y][j],dp[x][j-1]);
        }
    }
}

int main()
{
    int i,j;
    while(~scanf("%d",&n))
    {
        scanf("%s",s1);
        for(i=0;i<n;i++)
        {
            s2[i]=s1[n-1-i];
        }
        s2[i]='\0';
        lcs();
        printf("%d\n",n-dp[n%2][n]);
    }
    return 0;
}