#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1e9 + 7;
const long long INF = 1e18;
const long long nx[4] = {0, 0, 1, -1}, ny[4] = {1, -1, 0, 0};
void IO() {}
template <class T>
void unisort(vector<T>& v) {
  sort(begin(v), end(v));
  v.erase(unique(begin(v), end(v)), end(v));
}
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
long long lcm(long long a, long long b) { return (a * b) / gcd(a, b); }
void reverse(string& string) {
  long long n = string.length();
  for (long long i = 0; i < n / 2; i++) swap(string[i], string[n - i - 1]);
}
long long fact(long long nb) {
  long long res = 1;
  for (long long i = 2; i <= nb; i++) res *= i;
  return res;
}
bool sortbysec(const pair<long long, long long>& a,
               const pair<long long, long long>& b) {
  if (a.second == b.second) {
    return a.first < b.first;
  }
  return (a.second < b.second);
}
vector<string> v;
void subsequences(const string& a, const string& suffix) {
  if (a.length() >= 1) {
    v.push_back(a);
  }
  for (size_t i = 0; i < suffix.length(); ++i)
    subsequences(a + suffix[i], suffix.substr(i + 1));
}
int32_t main() {
  IO();
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  ;
  long long n, b, w;
  string s;
  char c;
  cin >> n >> s;
  for (long long i = 0; i < n; i++) {
    if (s[i] == 'W')
      w++;
    else
      b++;
  }
  if (w % 2 && b % 2) {
    cout << -1;
    return 0;
  }
  vector<long long> v;
  if (w % 2 == 0)
    c = 'B';
  else
    c = 'W';
  w = 0;
  for (long long i = 0; i < s.size(); i++) {
    if (w % 2 == 1) v.push_back(i);
    if (s[i] != c) w++;
  }
  cout << v.size() << "\n";
  for (long long i = 0; i < v.size(); i++) cout << v[i] << ' ';
  return 0;
}
