#include<bits/stdc++.h>
using namespace std;
int main()
{
  int p;
  int n,x,i,ar[n-1];
  string s;
  cin>>n>>s;
  char c[n+1];
  strcpy(c, s.c_str());
  for(i=0;i<n-1;i++)
  {
    if(c[i]=='B')
    {
      c[i]='W';
      if(c[i+1]=='B')
        c[i+1]='w';
      else
        c[i+1]='B';
      x++;
      ar[i]=i;
    }
  }
  if(c[i]=='B')
  {
    cout<<-1;
  }
  else{
  cout<<x<<endl;
  for(int i=0;i<n-1;i++)
    cout<<ar[i]<<" ";
  }
}
 

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