#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, i = 0, b = 0, w = 0;
  vector<long long int> v;
  cin >> n;
  char s[230];
  cin >> s;
  for (i = 0; i < n; i++) {
    if (s[i] == 'W')
      w++;
    else
      b++;
  }
  if (b % 2 == 1 && w % 2 == 1)
    cout << "-1" << endl;
  else {
    if (w % 2 == 0) {
      for (i = 0; i < n - 1;) {
        if (s[i] == 'W') {
          if (s[i + 1] == 'W') {
            v.push_back(i + 1);
            i += 2;
          } else {
            s[i + 1] = 'W';
            v.push_back(i + 1);
            i++;
          }
        } else
          i++;
      }
    } else {
      for (i = 0; i < n - 1;) {
        if (s[i] == 'B') {
          if (s[i + 1] == 'B') {
            v.push_back(i + 1);
            i += 2;
          } else {
            s[i + 1] = 'B';
            v.push_back(i + 1);
            i++;
          }
        } else
          i++;
      }
    }
    long long int x = v.size();
    cout << x << endl;
    for (i = 0; i < x; i++) cout << v[i] << " ";
    cout << endl;
  }
}
