from collections import defaultdict,deque
import sys,heapq,bisect,math,itertools,string,queue,copy,time
sys.setrecursionlimit(10**8)
INF = float('inf')
mod = 10**9+7
eps = 10**-7
def inp(): return int(sys.stdin.readline())
def inpl(): return list(map(int, sys.stdin.readline().split()))
def inpl_str(): return list(sys.stdin.readline().split())

import numpy as np

H,W = inpl()

AA = np.array([list(map(int,list(input()))) for _ in range(H)])

for x in range(W):
    tmp = sum(AA[:, x])
    if tmp == H or tmp == 0:
        break
else:
    print("YES")
    sys.exit()

for y in range(H):
    tmp = sum(AA[y, :])
    if tmp == W or tmp == 0:
        break
else:
    print("YES")
    sys.exit()

print("NO")