#include <bits/stdc++.h> using namespace std; using ll = long long; #include <ext/pb_ds/assoc_container.hpp> #include <ext/pb_ds/tree_policy.hpp> using namespace __gnu_pbds; template<class T> using o_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>; int main() { ll n; cin >> n; string s; cin >> s; ll r = 0, g = 0, y = 0; multiset<ll> R; multiset<ll> G; multiset<ll> Y; for(ll j = 0; j < n; j++){ char i = s[j]; if(i == 'R'){ r++; R.insert(j); }else if(i == 'G'){ g++; G.insert(j); }else if(i == 'Y'){ y++; Y.insert(j); } } if(max(max(r, g), y) > (n + 1)/2){ cout << -1 << endl; return 0; } string s1 = ""; string s2 = ""; for(ll i = 0; i < n; i++){ if(i%2 == 0){ s1 += "R"; s2 += "G"; }else{ s1 += "G"; s2 += "R"; } } o_set<ll> o1; o1.insert(999999); ll ans = 1e17; if(r == (n + 1)/2){ ll c1 = 0; for(ll i = 0; i < n; i++){ if(i%2 == 0){ auto t = *R.begin(); R.erase(R.begin()); ll minus = o1.order_of_key(t); c1 += t - minus; o1.insert(t); }else{ auto t = *G.begin(); G.erase(G.begin()); ll minus = o1.order_of_key(t); c1 += t - minus; o1.insert(t); } } ans = min(ans, c1); } o_set<ll> o2; o2.insert(999999); if(g == (n + 1)/2){ for(ll j = 0; j < n; j++){ char i = s[j]; if(i == 'R'){ R.insert(j); }else if(i == 'G'){ G.insert(j); }else if(i == 'Y'){ Y.insert(j); } } ll c1 = 0; for(ll i = 0; i < n; i++){ if(i%2 == 1){ auto t = *R.begin(); R.erase(R.begin()); ll minus = o2.order_of_key(t); c1 += t - minus; o2.insert(t); }else{ auto t = *G.begin(); G.erase(G.begin()); ll minus = o2.order_of_key(t); c1 += t - minus; o2.insert(t); } } ans = min(ans, c1); } cout << ans << endl; }