n, m = map(int, input().split())
ans = [-1]*n

if n = 1 and m = 0:
    print(0)
    exit()

for i in range(m):
    s, c = map(int, input().split())

    if s == 1 and c == 0:
        print(-1)
        exit()
        
    if ans[s-1] == -1 or ans[s-1] == c:
        ans[s-1] = c
    else:
        print(-1)
        exit()

if ans[0] == -1:
    ans[0] = 1

for i in range(n):
    if ans[i] == -1:
        ans[i] = 0

print(*ans, sep="")