n,m = map(int,input().split())
s = []
c = []
for i in range(m):
    val1,val2 = map(int,input().split())
    s.append(val1)
    c.append(val2)

digit = max(s) - min(s)

ans = []

for i in range(10 ** digit + 1,10 ** (digit + 1)):
    num = str(i)
    flg = 0
    for j in range(m):
        if num[s[j]-1] == str(c[j]):
            flg = 1
        else:
            flg = 0
            break
    if flg == 1:
        ans.append(i)

print(min(ans))