#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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