N,M=map(int,input().split())
First = 10**N-1
Answer =0
An = {}
box = []
for m in range(M):
    box.append(list(map(int,input().split())))
for m in range(M):
    if box[m][0] not in An:
        if box[m][0]  == 1 and box[m][1] == 0:
            Answer =-1
            break
        An[box[m][0]] = box[m][1]
    else:
        if An[box[m][0]] != box[m][1]:
            Answer =-1
            break
if 1 not in An and 2 in An:
    if An[2] == 0:
        Answer = -1
if Answer != -1:
    if 1 not in An:
        if 2 not in An:
            if 3 in An:
                Answer = An[3]
            else:
                Answer = -1
        else:
            An.setdefault(3,0)
            Answer = 10*An[2] + An[3]
    else:
        An.setdefault(3,0)
        An.setdefault(2,0)
        Answer = 100*An[1] + 10*An[2] + An[3]
print(Answer)