import sys
n,m = map(int,input().split())
s = [0] * m
c = [0] * m
for i in range(m):
    s[i],c[i] = map(int,input().split())
ans = [10] * max(s)
for i in range(m):
    if s[i] == 1 and c[i] == 0:
        print(-1)
        sys.exit()
    if ans[s[i] - 1] == 10:
        ans[s[i] - 1] = c[i]
    else:
        if c[i] != ans[s[i] - 1]:
            print(-1)
            sys.exit()
    
for i in range(len(ans)):
    if i == 0 and ans[i] == 10:
        ans[i] = 1
    elif ans[i] == 10:
        ans[i] = 0
print(''.join([str(i) for i in ans]))