from functools import lru_cache
N=int(input())
A=list(map(int,input().split()))
M=1000
cnt=[0]*M
for a in A:
    cnt[a]+=1
L,R=0,max(A)
@lru_cache(maxsize=None)
def solve(X,cnt,l,r):
    if max(cnt)==0:
        retu={X}
    elif l<r:
        retu=set()
        for d in range(M-1,-1,-1):
            if cnt[d]:
                for y in (d,R-d):
                    if l<y<r and max(R-d,d)==d:
                        cnt_=list(cnt)
                        ok=True
                        for x in X:
                            cnt_[abs(x-y)]-=1
                            if cnt_[abs(x-y)]<0:
                                ok=False
                        if ok:
                            retu|=solve(tuple(sorted(list(X)+[y])),tuple(cnt_),y,r)
                            retu|=solve(tuple(sorted(list(X)+[y])),tuple(cnt_),l,y)
                break
    return retu
cnt[R-L]-=1
ans_lst=solve(tuple([L,R]),tuple(cnt),L,R)
ans_lst=list(ans_lst)
le=len(ans_lst)
ans_lst.sort()
print(le)
for i in range(le):
    print(*ans_lst[i])