ll@n,y=0,z=0;
string@s;
rep(i,n-1){
	y|=s[i]=='B'&&s[i+1]=='B';
	z+=(s[i]=='A'||s[i+1]=='A')&&!(i>=1&&s[i-1]=='B'&&s[i+1]=='B');
}
wt(y+z);