#include <bits/stdc++.h>
using namespace std;
struct debugger {
  template <typename T>
  debugger& operator,(const T& v) {
    cerr << v << " ";
    return *this;
  }
} dbg;
inline long long gcd(long long a, long long b) {
  a = ((a) < 0 ? -(a) : (a));
  b = ((b) < 0 ? -(b) : (b));
  while (b) {
    a = a % b;
    swap(a, b);
  }
  return a;
}
long long ext_gcd(long long A, long long B, long long* X, long long* Y) {
  long long x2, y2, x1, y1, x, y, r2, r1, q, r;
  x2 = 1;
  y2 = 0;
  x1 = 0;
  y1 = 1;
  for (r2 = A, r1 = B; r1 != 0;
       r2 = r1, r1 = r, x2 = x1, y2 = y1, x1 = x, y1 = y) {
    q = r2 / r1;
    r = r2 % r1;
    x = x2 - (q * x1);
    y = y2 - (q * y1);
  }
  *X = x2;
  *Y = y2;
  return r2;
}
inline long long modInv(long long a, long long m) {
  long long x, y;
  ext_gcd(a, m, &x, &y);
  x %= m;
  if (x < 0) x += m;
  return x;
}
inline long long bigmod(long long a, long long p, long long m) {
  long long res = 1 % m, x = a % m;
  while (p) {
    if (p & 1) res = (res * x) % m;
    x = (x * x) % m;
    p >>= 1;
  }
  return res;
}
const long long inf = 2147383647;
const long long mod = 1000000007;
const double pi = 2 * acos(0.0);
const double eps = 1e-11;
vector<int> V1, V2;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  cin >> n;
  string str;
  cin >> str;
  if (str.size() == 1) {
    cout << "0\n";
    return 0;
  }
  string S1 = str, S2 = str;
  for (int i = 0; i < S1.size() - 1; i++) {
    if (S1[i] == 'B' && S1[i + 1] == 'B') {
      S1[i] = 'W';
      S1[i + 1] = 'W';
      V1.push_back(i + 1);
    } else if (S1[i] == 'B' && S1[i + 1] == 'W') {
      S1[i] = 'W';
      S1[i + 1] = 'B';
      V1.push_back(i + 1);
    }
  }
  if (S1[S1.size() - 1] == 'W') {
    cout << V1.size() << "\n";
    for (int i = 0; i < V1.size(); i++) {
      if (i != 0) cout << " ";
      cout << V1[i];
    }
    if (V1.size() > 0) cout << "\n";
    return 0;
  }
  for (int i = 0; i < S2.size() - 1; i++) {
    if (S2[i] == 'W' && S2[i + 1] == 'W') {
      S2[i] = 'B';
      S2[i + 1] = 'B';
      V2.push_back(i + 1);
    } else if (S2[i] == 'W' && S2[i + 1] == 'B') {
      S2[i] = 'B';
      S2[i + 1] = 'W';
      V2.push_back(i + 1);
    }
  }
  if (S2[S2.size() - 1] == 'B') {
    cout << V2.size() << "\n";
    for (int i = 0; i < V2.size(); i++) {
      if (i != 0) cout << " ";
      cout << V2[i];
    }
    if (V2.size() > 0) cout << "\n";
    return 0;
  }
  cout << "-1\n";
  return 0;
}
