#include <bits/stdc++.h>
using namespace std;
template <class C>
void min_self(C &a, C b) {
  a = min(a, b);
}
template <class C>
void max_self(C &a, C b) {
  a = max(a, b);
}
long long mod(long long n, long long m = 1000000007) {
  n %= m, n += m, n %= m;
  return n;
}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
unordered_map<long long, int, custom_hash> safe_map;
const int MAXN = 1e5 + 5;
const int LOGN = 21;
const long long INF = 1e14;
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  string s;
  cin >> n >> s;
  vector<int> ans;
  for (int i = 0; i < n; i++) {
    if (s[i] != 'W' && i + 1 < n) {
      ans.push_back(i);
      s[i] = 'W' + 'B' - s[i];
      s[i + 1] = 'W' + 'B' - s[i + 1];
    }
  }
  int imp = 0;
  for (int i = 0; i < n; i++) {
    if (s[i] != 'W') {
      imp = 1;
      break;
    }
  }
  if (imp) {
    for (int i = 0; i < n; i++) {
      if (s[i] != 'B' && i + 1 < n) {
        ans.push_back(i);
        s[i] = 'B' + 'W' - s[i];
        s[i + 1] = 'B' + 'W' - s[i + 1];
      }
    }
    int no = 0;
    for (int i = 0; i < n; i++) {
      if (s[i] != 'B') {
        no = 1;
        break;
      }
    }
    if (no) {
      cout << -1, cout << "\n";
    } else {
      cout << ans.size(), cout << "\n";
      for (auto x : ans) cout << x + 1 << " ";
    }
  } else {
    cout << ans.size(), cout << "\n";
    for (auto x : ans) cout << x + 1 << " ";
  }
  cerr << "\nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "ms\n";
  return 0;
}
