n,m = map(int,input().split())
sc = [0]*m
for i in range(m):
    sc[i] = list(map(int,input().split()))
ans = 10**5
for i in range(10**(n-1),10**n):
    x = list(str(i))
    sw = 1
    for j in range(m):
        if x[sc[j][0]-1] == str(sc[j][1]):
            pass
        else:
            sw = 0
            break
    if sw == 1:
        ans = min(ans,i)
if ans == 10**5:
    print(-1)
else:
    print(ans)