ll@n;string@s;
ll a[n+1],c[n+1];
a[0]=0;
rep(i,n){
	a[i+1]=a[i]+(s[i]!='C');
}
c[n]=0;
rrep(i,n){
	c[i]=c[i+1]+(s[i]!='A');
}
ll u=0,v=0;
rep(i,n){
	if(s[i]=='A'||s[i]=='?'&&a[i]<c[i+1]){
		u+=1;
	}else{
		v+=u;
	}
}
wt(v);