ll@N,@M,@A[N*2+1],b[N+1]{},j,t;list<ll>S;rep(M){ll@s;b[s]=1;S.push_back(s);}auto T=S;while(T.size()){j=T.front();for(auto i=S.begin(),e=S.end();i!=e;i++){if(!b[t=A[*i+j]])b[t]=1,T.push_back(t);}T.pop_front();}wt(sum[i,0,N+1](b[i]));