#include<iostream> #include<cstdio> #include<queue> #include<string> using namespace std; struct status { string str; int time; status() {} status(string s, int t) :str(s), time(t) {} }; string swap(string s, int a, int b) { string str = s; str[a] = s[b]; str[b] = s[a]; return str; } int BFS(string str) { queue<status> myQueue; myQueue.push(status(str, 0)); while (!myQueue.empty()) { status current = myQueue.front(); myQueue.pop(); if (current.str.find("2012") != string::npos) return current.time; else { for (int i = 0; i < str.size() - 1; ++i) myQueue.push(status(swap(current.str, i, i + 1), current.time + 1)); } } return -1; } int main() { int n, count_0, count_1, count_2; string str; while (cin>>n>>str) { count_0 = count_1 = count_2 = 0; for (int i = 0; i < n; ++i) { if (str[i] == '0')++count_0; else if (str[i] == '1')++count_1; else ++count_2; } if (count_0 < 1 || count_1 < 1 || count_2 < 2) printf("%d\n", -1); else { printf("%d\n", BFS(str)); } } return 0; }