N, M = list(map(int,input().split()))
s = []
c = []
for i in range(M):
    in1, in2 = list(map(int,input().split()))
    s.append(in1 - 1)
    c.append(in2)
    
def solve():
    
    res = [-1 for _ in range(N)]

    for i in range(M):
        if res[s[i]] != -1 and res[s[i]] != c[i]:
            print(-1)
            return
        if s[i] == 0 and c[i] == 0:
            print(-1)
            return
        res[s[i]] = c[i] 

    ans = ""
    for i in range(N):
        if res[i] == -1:
            if i == 0:
                ans += "1"
            else:
                ans += "0"
        else:
            ans += str(res[i])
    print(ans)

else:
    solve()