1 #include <cstdio>
 2 #include <cstring>
 3 #include <iostream>
 4 using namespace std;
 5 char a[5050], b[5050]; 
 6 int dp[2][5050];
 7 int main()
 8 {
 9     int n;
10     while(~scanf("%d", &n))
11     {
12         scanf("%s", b);
13         strcpy(a, b);
14         strrev(b);
15         memset(dp, 0, sizeof(dp));           //+F+++U++++K++
16         for(int i = 1; i <= n; i++)
17             for(int j = 1; j <= n; j++)
18             {
19                 if(a[i-1] == b[j-1])
20                     dp[i%2][j] = dp[(i-1)%2][j-1] + 1;
21                 else
22                     dp[i%2][j] = max(dp[(i-1)%2][j], dp[i%2][j-1]);
23             }
24             printf("%d\n", n - dp[n%2][n]);
25     }
26     return 0;   
27 }