#include <iostream>
int main(){
	int D;
	std::cin>>D;
	int x=0,y=0,z=0,a;
	for(int i=0;i<=D;D++){std::cin>>a;x+=(i%2?-a:a);y+=a;if(i==0)z=a;}
	int b[3];b[0]=z;b[1]=(y-x)/2;b[2]=(x+y)/2-z;
	int l=1;if(b[1])l=2;if(b[2])l=3;
	std::cout<<l-1<<"\n";
	for (int i = 0; i < l; i++) {
	std::cout<<b[i]<<" ";
	}
	std::cout<<"\n";
	return 0;
}