#include <bits/stdc++.h> #define L(i, j, k) for(int i = (j); i <= (k); i++) #define R(i, j, k) for(int i = (j); i >= (k); i--) #define ll long long #define sz(a) ((int) a.size()) #define all(a) a.begin(), a.end() #define vi vector<ll> #define pb emplace_back #define me(a, x) memset(a, x, sizeof(a)) #define fst first #define snd second #define ii pair<int, int> using namespace std; int n; bool valid(string s){ for(int i=1;i<n;i++){ if(s[i]==s[i-1])return false; } return true; } int main(){ ios::sync_with_stdio(false); cin.tie(nullptr); cin>>n; string s;cin>>s; if(valid(s)){cout<<0<<endl;return 0;} queue<string>q; q.push(s); int ans=1e9; unordered_map<string,int>d,v; d[s]=0; v[s]=1; while(sz(q)){ string u=q.front();q.pop(); if(d[u]==((n+1)*n)/2)continue; for(int i=1;i<n;i++){ string c=u; swap(c[i],c[i-1]); if(v[c]==1)continue; d[c]=d[u]+1; if(valid(c)){ ans=min(ans,d[c]); } v[c]=1; q.push(c); } } if(ans==1e9)cout<<-1<<endl; else cout<<ans<<endl; } //1 2 3 //3 1 2