1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <iostream>
 5 #include <vector>
 6 #include <queue>
 7 #include <cmath>
 8 #include <set>
 9 using namespace std;
10 
11 #define N 5005
12 
13 int max(int x,int y){return x>y?x:y;}
14 int min(int x,int y){return x<y?x:y;}
15 int abs(int x,int y){return x<0?-x:x;}
16 
17 
18 int dp[2][N];
19 int n;
20 char s[N];
21 
22 main()
23 {
24     int i, j, k;
25     while(scanf("%d",&n)==1){
26         memset(dp,0,sizeof(dp));
27         scanf("%s",s+1);
28         char s1[N];
29         for(i=n;i>=1;i--) s1[i]=s[n-i+1];
30         int maxh=0;
31         for(i=1;i<=n;i++){
32             memset(dp[i&1],0,sizeof(dp[i&1]));
33             for(j=1;j<=n;j++){
34                 if(s[i]==s1[j]){
35                     dp[i&1][j]=max(dp[!(i&1)][j-1]+1,dp[i&1][j]);
36                 }
37                 else dp[i&1][j]=max(dp[!(i&1)][j],dp[i&1][j-1]);
38                 maxh=max(maxh,dp[i&1][j]);
39             }
40         }
41         printf("%d\n",n-maxh);
42     }
43 }