#include<stdio.h>
long int x[50001],a[50001],n,i,k;
int main()
{
	FILE *f,*g;
	f=fopen("reguli.in","r");
	g=fopen("reguli.out","w");
	fscanf(f,"%ld",&n);
	for(i=0;i<n;i++)fscanf(f,"%ld",&x[i]);
	for(i=0;i<n;i++)a[i]=x[i+1]-x[i];
	for(i=1;i<n;i++)if(a[1]!=a[i])k++;
	for(i=0;i<n;i++)x[i+1]=x[i]+a[i];
	fprintf(g,"%ld",k);
	for(i=0;i<k;i++)fprintf(g,"%ld",a[i]);
	fcloseall();
	return 0;
}