#include < iostream >
using   namespace  std;

int  n;
short  f[ 5001 ][ 5001 ] = { 0 };
char  s[ 5000 ];
int  main()
{
    scanf( " %d " , & n); getchar();
    gets(s);
     for ( int  i = 1 ;i <= n; ++ i)
         for ( int  j = 1 ;j <= n; ++ j)
             if (s[i - 1 ] != s[n - j]){
                 if (f[i][j - 1 ] > f[i - 1 ][j])
                    f[i][j] = f[i][j - 1 ];
                 else  f[i][j] = f[i - 1 ][j];
            }
             else  f[i][j] = f[i - 1 ][j - 1 ] + 1 ;
    printf( " %d\n " ,n - f[n][n]);
     return   0 ;
}