#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<string>
#include<string.h>
#include<stdlib.h>
#include<vector>
#include<math.h>
#include<map>
#include<queue>
using namespace std;

bool check(string s){
    int n = (int)s.length();
    for(int i=0;i<n-3;i++){
        if(s.substr(i,4) == "2012") return true;
    }
    return false;
}
int main(){
    int n;
    string s;
    cin>>n>>s;
    map<string,int> mp;
    queue<string> q;
    q.push(s);
    int res = -1;
    mp[s] = 0;
    string ns;
    while(!q.empty()){
        string top = q.front();
        q.pop();
        if(check(top)){
            res = mp[top];
            break;
        }
        int n = (int)top.length();
        int step = mp[top];
        for(int i=0;i<n-1;i++){
            swap(top[i], top[i+1]);
            if(mp.find(top) == mp.end()){
                q.push(top);
                mp[top] = step+1;
            }
            swap(top[i], top[i+1]);
        }
    }

    printf("%d\n",res);

    return 0;
}