1 #include<iostream>
  2 #include<cstdio>
  3 #include<string>
  4 #include<cstring>
  5 #include<queue>
  6 using namespace std;
  7 
  8 const int maxn=5000000;
  9 string s1,s2;
 10 struct Trie //字典树查询字符串
 11 {
 12     int ch[maxn][4];
 13     int sz; //结点总数
 14     void clear(){sz=1;memset(ch[0],0,sizeof(ch[0]));}
 15     int Num(char ch)
 16     {
 17         if(ch==‘A‘) return 0;
 18         if(ch==‘C‘) return 1;
 19         if(ch==‘G‘) return 2;
 20         if(ch==‘T‘) return 3;
 21     }
 22     void insert(string s)
 23     {
 24         int len=s.size(),u=0;
 25         for(int i=0;i<len;i++)
 26         {
 27             int c=Num(s[i]);
 28             if(!ch[u][c])
 29             {
 30                 memset(ch[sz],0,sizeof(ch[sz]));
 31                 ch[u][c]=sz++;
 32             }
 33             u=ch[u][c];
 34         }
 35     }
 36     int Find(string s)
 37     {
 38         int u = 0,len=s.size();
 39         for(int i = 0; i < len; i++)
 40         {
 41             int c = Num(s[i]);
 42             if(!ch[u][c]) return 0;
 43             u = ch[u][c];
 44         }
 45         return 1;
 46     }
 47 }trie;
 48 struct point //队列数据
 49 {
 50     string s;
 51     int step;
 52 };
 53 void swap(char &a,char &b)
 54 {
 55     char t=a;
 56     a=b;
 57     b=t;
 58 }
 59 string change1(string s)
 60 {
 61     swap(s[0],s[1]);
 62     return s;
 63 }
 64 string change2(string s)
 65 {
 66     char ch=s[0];
 67     s.erase(s.begin());
 68     s+=ch;
 69     return s;
 70 }
 71 void solve()
 72 {
 73     trie.clear();
 74     queue<point> Q;
 75     point p,t;
 76     t.s=s1;t.step=0;
 77     trie.insert(t.s);
 78     Q.push(t);
 79     while(!Q.empty())
 80     {
 81         t=Q.front();Q.pop();
 82         p.step=t.step+1;
 83         p.s=change1(t.s);
 84         if(!trie.Find(p.s))
 85         {
 86             if(p.s==s2)
 87             {
 88                 printf("%d\n",p.step);
 89                 return ;
 90             }
 91             Q.push(p);
 92             trie.insert(p.s);
 93         }
 94         p.s=change2(t.s);
 95         if(!trie.Find(p.s))
 96         {
 97             if(p.s==s2)
 98             {
 99                 printf("%d\n",p.step);
100                 return ;
101             }
102             Q.push(p);
103             trie.insert(p.s);
104         }
105     }
106     return ;
107 }
108 int main()
109 {
110     int n;
111     while(~scanf("%d",&n))
112     {
113         cin>>s1>>s2;
114         if(s1==s2)
115         {
116             printf("0\n");
117             continue;
118         }
119         solve();
120     }
121     return 0;
122 }