N, M = map(int, input().split())
S = [0]*M
C = [0]*M
SC = {1: set([]), 2: set([]), 3: set([])}
for m in range(M):
    S[m], C[m] = map(int, input().split())
    SC[S[m]].add(C[m])

ANS = [0]*N
out = 0
for i in range(1, 4):
    if len(SC[i]) >= 2:
        out = 1
if out == 1:
    print(-1)
else:
    for i in range(N):
        if i == 0:
            if list(SC[1])[0] == 0:
                out = 1
            elif len(SC[1]) == 0:
                ANS[0] = 1
            else:
                ANS[0] = list(SC[1])[0]
        else:
            if len(SC[i+1]) == 0:
                ANS[i] = 0
            else:
                ANS[i] = list(SC[i+1])[0]

    if ANS[0] == 0:
        print(-1)
    else:

        ans = 0
        for i in range(N):
            ans += ANS[i]*10**(N-i-1)

        print(ans)