1 #include <cstdio> 2 #include <cstring> 3 #include <algorithm> 4 #define ll __int64 5 using namespace std; 6  7 int n; 8 char str[100]; 9 10 int main()11 {12    while(scanf("%d",&n)!=EOF)13    {14       scanf("%s",str);15       int k=strlen(str);16       ll ans=0;17       ll s=1;18       for(int i=0; i<k; i++)19       {20           if(str[i]==‘B‘)21           {22               ans+=s;23           }24           s*=2;25       }26       printf("%I64d\n",ans);27    }28    return 0;29 }