N, M = map(int, input().split(" "))

ans = 0
sici = []
check = [[] for i in range(3)]
for i in range(M):
    si, ci = map(int, input().split(" "))
    sici.append([si, ci])
    if not ci in check[si-1]:
        check[si-1].append(ci)
        if len(check[si-1]) > 1:
            ans = -1
            break
    for si, ci in sici:
        if si > N:
            ans = -1
            break
        if ci == 0 and si == 1 and N > 1:
            ans = -1
            break
        if si == 1:
            if N == 1:
                if ans == 0:
                    ans += ci
                elif ans == ci:
                    continue
                else:
                    ans = -1
                    break

            if N == 2:
                if ans//10 == 0:
                    ans += ci * 10
                elif ans//10 == ci:
                    continue
                else:
                    ans = -1
                    break
            
            if N == 3:
                if ans//100 == 0:
                    ans += ci * 100
                elif ans//100 == ci:
                    continue
                else:
                    ans = -1
                    break
        elif si == 2:
            if N == 2:
                if ans%10 == 0:
                    ans += ci
                elif ans%10 == ci:
                    continue
                else:
                    ans = -1
                    break
            if N == 3:
                if (ans%100)//10 == 0:
                    ans += ci * 10
                elif (ans%100)//10 == ci:
                    continue
                else:
                    ans = -1
                    break
        elif si == 3 and N == 3:
            if ans%10 == 0:
                ans += ci
            elif ans%10 == ci:
                continue
            else:
                ans = -1
                break

if ans < 100 and N == 3:
    ans = -1
if ans < 10 and N == 2:
    ans = -1
print(ans)