#include <bits/stdc++.h>
using namespace std;
const int maxx = 210;
char s[maxx];
int ans[maxx];
int main() {
  int n;
  scanf("%d", &n);
  scanf("%s", s + 1);
  int t = 0;
  for (int i = 1; i < n; i++) {
    if (s[i] == 'W') {
      s[i] = 'B';
      if (s[i + 1] == 'W')
        s[i + 1] = 'B';
      else
        s[i + 1] = 'W';
      ans[++t] = i;
    }
  }
  if (s[n] == 'B') {
    printf("%d\n", t);
    for (int i = 1; i <= t; i++) printf("%d ", ans[i]);
    printf("\n");
  } else {
    if (n % 2) {
      for (int i = 1; i < n; i += 2) ans[++t] = i;
      printf("%d\n", t);
      for (int i = 1; i <= t; i++) printf("%d ", ans[i]);
      printf("\n");
    } else
      printf("-1\n");
  }
  return 0;
}
