#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;
string s;
int a[maxn], tot, n;
int main() {
  while (cin >> n) {
    memset(a, 0, sizeof a);
    tot = 0;
    cin >> s;
    string temp = s;
    if (n == 1) {
      puts("0");
      continue;
    }
    for (int i = n - 1; i >= 1; i--) {
      if (s[i] == 'B')
        s[i] = 'W', s[i - 1] = (s[i - 1] == 'B' ? 'W' : 'B'), a[++tot] = i - 1;
    }
    if (s[0] == 'B') {
      tot = 0;
      s = temp;
      for (int i = n - 1; i >= 1; i--) {
        if (s[i] == 'W')
          s[i] = 'B', s[i - 1] = (s[i - 1] == 'B' ? 'W' : 'B'),
          a[++tot] = i - 1;
      }
      if (s[0] == 'W')
        puts("-1");
      else {
        cout << tot << endl;
        for (int i = 1; i <= tot; i++) cout << a[i] + 1 << " ";
        cout << endl;
      }
    } else {
      cout << tot << endl;
      for (int i = 1; i <= tot; i++) cout << a[i] + 1 << " ";
      cout << endl;
    }
  }
}
