import sys
import numpy as np

N, M = [int(_) for _ in input().split()]
S, C = np.array([[int(_) for _ in input().split()] for i in range(M)]).T

print("no")
# ans = [-1] * N

# for i in range(M):
#     j = int(S[i]) - 1
#     if ans[j] == -1 or ans[j] == C[i]:
#         ans[j] = C[i]
#     else:
#         print("-1")
#         sys.exit()

# if ans[0] == -1:
#     ans[0] = 1

# for i in range(1, N):
#     if ans[i] == -1:
#         ans[i] = 0

# s = "".join(map(str, ans))

# if int(s) == 0:
#     print("-1")
# else:
#     print(s)
