#pragma GCC optimize("Ofast")

#define rd_skip() while(*rp++>=48)
#define wt(v) {ulong _z=v;do*--wp=_z%10+48;while(_z/=10);}

typedef unsigned long ulong;

int main(){
	char*mmap();
	char*rp=mmap(0l,1l<<25,1,2,0,0ll);
	rd_skip();
	long y=0,z=0;
	long e=*rp++=='B';
	long d=*rp++=='B';
	long c;
	while(c=*rp++){
		c=c=='B';
		y|=e&d;
		z+=!(e&d|e&c);
		e=d;d=c;
	}
	z+=y;
	char wbuf[64],*wp=wbuf+sizeof wbuf;
	wt(z);
	write(1,wp,wbuf+sizeof wbuf-wp);
	_exit(0);
}