#include <bits/stdc++.h>
using namespace std;
long long int INF = 1e18;
const long long fact_table = 5000000;
double Pi = 3.1415926535897932384626;
vector<long long> G[550010];
vector<pair<long long, double> > tree[500010];
priority_queue<long long> pql;
priority_queue<pair<long long, long long> > pqp;
priority_queue<long long, vector<long long>, greater<long long> > pqls;
priority_queue<pair<long long, long long>, vector<pair<long long, long long> >,
               greater<pair<long long, long long> > >
    pqps;
int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
int dy[8] = {0, 1, 0, -1, 1, -1, -1, 1};
char dir[] = "DRUL";
long long mod = 1000000007;
long long rui(long long number1, long long number2) {
  if (number2 == 0) {
    return 1;
  } else {
    long long number3 = rui(number1, number2 / 2);
    number3 *= number3;
    number3 %= mod;
    if (number2 % 2 == 1) {
      number3 *= number1;
      number3 %= mod;
    }
    return number3;
  }
}
long long gcd(long long number1, long long number2) {
  if (number1 > number2) {
    swap(number1, number2);
  }
  if (number1 == 0 || number1 == number2) {
    return number2;
  } else {
    return gcd(number2 % number1, number1);
  }
}
void YES(bool condition) {
  if (condition) {
    cout << "YES"
         << "\n";
    ;
  } else {
    cout << "NO"
         << "\n";
    ;
  }
  return;
}
void Yes(bool condition) {
  if (condition) {
    cout << "Yes"
         << "\n";
    ;
  } else {
    cout << "No"
         << "\n";
    ;
  }
  return;
}
long long n, m, num, sum, a, b, c, d, e, f, g, h, w, i, j, q, r, l;
long long k, ans;
long long x[500005], y[500005], z[500005];
bool used[500005];
char s[500005];
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n;
  cin >> s;
  long long white = 0, black = 0;
  for (long long i = 0; i < n; i++) {
    if (s[i] == 'W') {
      white++;
      x[i] = 2;
    } else {
      black++;
      x[i] = 1;
    }
  }
  if (n % 2 == 0) {
    if (white % 2 == 1) {
      cout << "-1"
           << "\n";
      ;
    } else {
      vector<long long> operation;
      for (long long i = 0; i < n - 1; i++) {
        if (x[i] == 1) {
          operation.push_back(i + 1);
          x[i] = 3 - x[i];
          x[i + 1] = 3 - x[i + 1];
        }
      }
      cout << operation.size() << "\n";
      ;
      if (operation.size() == 0) {
        return 0;
      }
      for (long long i = 0; i < operation.size(); i++) {
        cout << (operation[i]) << " ";
        ;
      }
      cout << "\n";
      ;
      return 0;
    }
  } else {
    vector<long long> operation;
    if (white % 2 == 1) {
      for (long long i = 0; i < n - 1; i++) {
        if (x[i] == 1) {
          operation.push_back(i + 1);
          x[i] = 3 - x[i];
          x[i + 1] = 3 - x[i + 1];
        }
      }
      cout << operation.size() << "\n";
      ;
      if (operation.size() == 0) {
        return 0;
      }
      for (long long i = 0; i < operation.size(); i++) {
        cout << (operation[i]) << " ";
        ;
      }
      cout << "\n";
      ;
      return 0;
    } else {
      for (long long i = 0; i < n - 1; i++) {
        if (x[i] == 2) {
          operation.push_back(i + 1);
          x[i] = 3 - x[i];
          x[i + 1] = 3 - x[i + 1];
        }
      }
      cout << operation.size() << "\n";
      ;
      if (operation.size() == 0) {
        return 0;
      }
      for (long long i = 0; i < operation.size(); i++) {
        cout << (operation[i]) << " ";
        ;
      }
      cout << "\n";
      ;
      return 0;
    }
  }
  return 0;
}
