#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1e6 + 10;
const int mod = 998244353;
const int INF = 0x3f3f3f3f;
char s[300];
int main() {
  int n;
  scanf("%d", &n);
  scanf("%s", s);
  int w = 0, b = 0;
  for (int i = 0; i < n; i++) {
    if (s[i] == 'W')
      w++;
    else
      b++;
  }
  if (w % 2 == 1 && b % 2 == 1)
    printf("-1\n");
  else if (w == 0 || b == 0) {
    printf("0\n");
  } else {
    int d[300];
    memset(d, 0, sizeof(d));
    int op = b % 2 == 0 ? 1 : 2;
    int tot = 0;
    for (int i = 0; i + 1 < n; i++) {
      if (op == 1 && s[i] == 'B') {
        s[i] = 'W', s[i + 1] = s[i + 1] == 'B' ? 'W' : 'B', d[tot++] = i + 1;
      } else if (op == 2 && s[i] == 'W') {
        s[i] = 'B', s[i + 1] = s[i + 1] == 'W' ? 'B' : 'W', d[tot++] = i + 1;
      }
    }
    printf("%d\n", tot);
    for (int i = 0; i < tot; i++) {
      if (i == 0)
        printf("%d", d[i]);
      else
        printf(" %d", d[i]);
    }
  }
}
