
N,M=map(int,input().split())
s=[]
c=[]
for i in range(M):
    a, b = map(int,input().split())
    s.append(a)
    c.append(b)

okflag = True

for i in range(M):

    if not okflag:
         break
    for j in range(M):
     if not okflag:
         break
     if not (i==j):

        if s[i]==s[j] and c[i]!=c[j]:

            okflag = False
            print("No")

if okflag:
    answer = ["0"] * N
    for i in range(M):
        answer[s[i]] = str(c[i])
    if not N == 1 and answer[0] == "0":
        answer[0] = "1"
    result = ''.join(answer)
    print(result)
    
