#include <cstdio>
#include <list>
#define NMAX 500001
using namespace std;

int V[NMAX],aparitii[NMAX];
int n,x1,x2,nr;
list <int> L;

int main(){

    freopen("reguli.in","r",stdin);
    freopen("reguli.out","w",stdout);
    scanf("%d",&n);
    scanf("%d",&x1);
    for(register int i=1;i<n;++i){
        scanf("%d",&x2);
        if(!aparitii[x2-x1]){
            nr++;
        L.push_back(x2-x1);
        }
        aparitii[x2-x1]++;
              x1 = x2;
            }

    printf("%d\n",nr);
    for(list<int>::iterator it = L.begin();it!=L.end();++it)
        printf("%d\n",*it);

return 0;
}