ll@n,@m,@a[2n+1],@s[m],t[n+1]{},q[n+1],r=0;
rep(j,m){
	ll b=s[j];
	t[b]=1;
	q[r++]=b;
}
while(r){
	ll b=q[--r];
	rep(j,m){
		ll c=s[j];
		ll d=a[b+c];
		if(!t[d]){
			t[d]=1;
			q[r++]=d;
		}
	}
}
wt(sum(t(n+1)));