#include <bits/stdc++.h>
using namespace std;
const long long int maxn = 1e5 + 6;
const long long int MOD = 1e9 + 7;
vector<int> prim(1000005, 1);
int fact[maxn];
long long int binomialCoeff(long long int n, long long int k) {
  long long int res = 1;
  if (k > n - k) k = n - k;
  for (long long int i = 0; i < k; ++i) {
    res *= (n - i);
    res /= (i + 1);
  }
  return res;
}
bool isVowel(char ch) {
  if (ch == 'a' || ch == 'i' || ch == 'e' || ch == 'u' || ch == 'o') {
    return true;
  }
  return false;
}
long long int power(long long int x, long long int i, long long int mod) {
  long long int ans = 1;
  while (i > 0) {
    if (i & 1) ans = (ans * x) % mod;
    i >>= 1;
    x = (x * x) % mod;
  }
  return ans;
}
long long int modInverse(long long int x, long long int mod) {
  return power(x, mod - 2, mod);
}
int nCr(int n, int r) {
  if (n < r) {
    return 0;
  }
  return (((fact[n] * modInverse(fact[n - r], MOD)) % MOD) *
          modInverse(fact[r], MOD)) %
         MOD;
}
long long int power(int x, unsigned int y) {
  long long int temp;
  if (y == 0) return 1;
  temp = power(x, y / 2);
  if (y % 2 == 0)
    return temp * temp;
  else
    return x * temp * temp;
}
void erath(int n) {
  prim[1] = 0;
  prim[0] = 0;
  prim[2] = 1;
  for (int i = 2; i * i <= n; i++) {
    if (prim[i]) {
      for (int j = i * i; j <= n; j += i) {
        prim[j] = 0;
      }
    }
  }
}
long long int gcd(long long int a, long long int b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long int lcm(long long int a, long long int b) {
  return (a / gcd(a, b)) * b;
}
bool sortbysec(const pair<int, int> &a, const pair<int, int> &b) {
  return (a.second < b.second);
}
long long int n, m, k;
int getmid(int l, int r) { return (l + (r - l) / 2); }
struct segtree {
  int siz;
  vector<pair<long long int, long long int> > sums;
  void init(int n) {
    siz = 1;
    while (siz < n) siz *= 2;
    sums.assign(2 * siz, {LONG_MAX, 0});
  }
  void set(int i, int v, int cur, int l, int r) {
    if (r - l == 1) {
      sums[cur].first = v;
      sums[cur].second = 1;
      return;
    }
    int m = getmid(l, r);
    if (i < m) {
      set(i, v, 2 * cur + 1, l, m);
    } else
      set(i, v, 2 * cur + 2, m, r);
    sums[cur].first = min(sums[2 * cur + 1].first, sums[2 * cur + 2].first);
    if (sums[2 * cur + 1].first == sums[cur].first &&
        sums[2 * cur + 2].first == sums[cur].first) {
      sums[cur].second = sums[cur * 2 + 1].second + sums[cur * 2 + 2].second;
    } else if (sums[2 * cur + 1].first == sums[cur].first) {
      sums[cur].second = sums[cur * 2 + 1].second;
    } else {
      sums[cur].second = sums[cur * 2 + 2].second;
    }
  }
  void set(int i, int v) { set(i, v, 0, 0, siz); }
  pair<long long int, long long int> sum(int l, int r, int cur, int lx,
                                         int rx) {
    if (lx >= r || l >= rx) return {LONG_MAX, 0};
    if (lx >= l && rx <= r) return {sums[cur].first, sums[cur].second};
    int mid = getmid(lx, rx);
    pair<long long int, long long int> s1 = sum(l, r, 2 * cur + 1, lx, mid),
                                       s2 = sum(l, r, 2 * cur + 2, mid, rx);
    if (s1.first < s2.first) {
      return s1;
    } else if (s1.first > s2.first)
      return s2;
    else
      return {s1.first, s1.second + s2.second};
  }
  pair<long long int, long long int> sum(int l, int r) {
    return sum(l, r, 0, 0, siz);
  }
};
vector<int> gr[100000];
void ans() {
  cin >> n;
  string s;
  cin >> s;
  int bl = 0, wh = 0;
  for (auto it : s) {
    if (it == 'W') wh++;
  }
  bl = n - wh;
  if (bl == 0 || bl == n) {
    cout << 0 << endl;
  } else if (bl % 2 == 1 && wh % 2 == 1) {
    cout << -1 << endl;
  } else {
    int pos;
    char c;
    int i = 0, j = n - 1;
    if (bl % 2 == 0) {
      c = 'B';
      pos = bl;
    } else {
      c = 'W';
      pos = wh;
    }
    vector<long long int> ans;
    while (j > 0) {
      if (s[j] == c) {
        if (s[j - 1] != c) {
          ans.push_back(j);
          swap(s[j - 1], s[j]);
        } else {
          ans.push_back(j);
          j--;
        }
      }
      j--;
    }
    cout << ans.size() << endl;
    for (auto it : ans) cout << it << " ";
    cout << endl;
  }
}
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int t = 1;
  while (t--) {
    ans();
  }
  return 0;
}
