import sys
n,m = map(int,input().split())
ans = [-1 for i in range(n)]
if n == 1:
    if m == 0:
        print(0)
        sys.exit()
    else:
        s,c = map(int,input().split())
        print(c)
        sys.exit()
else:
    for i in range(m):
        s,c = map(int,input().split())
        if s-1 == 0:
            if c == 0:
                print(-1)
                sys.exit()
            else:
                if ans[s-1] == -1:
                    ans[s-1] = c
                else:
                    if c == ans[s-1]:
                        continue
                    else:
                        print(-1)
                        sys.exit()
        else:
            if ans[s-1] == -1:
                    ans[s-1] = c
            else:
                if c == ans[s-1]:
                    continue
                else:
                    print(-1)
                    sys.exit()
    if ans[0] == -1:
        ans[0] = 1
    for i in range(n):
        if ans[i] == -1:
            ans[i] = 0
    ans2 = ""
    for i in range(n):
        ans2 += str(ans[i])
    print(ans2)
