import sys
input = sys.stdin.readline

h, w = map(int, input().split())
grid = []
for _ in range(h):
    line = input().rstrip('\n')
    grid.append(line)

flg_h0 = 0
flg_h1 = 0
flg_w0 = 0
flg_w1 = 0
# print(grid)
for i in range(h):
    if grid[i].count('0') == 0:
        flg_h1 = 1
    if grid[i].count('0') == w:
        flg_h0 = 1
for i in range(w):
    cnt = 0
    for j in range(h):
        if grid[j][i] == '0':
            cnt += 1
    if cnt == 0:
        flg_w1 = 1
    if cnt == h:
        flg_w0 = 1

# print(flg_w0, flg_w1, flg_h0, flg_h1)

if flg_h0 and flg_w0:
    print('NO')
elif flg_h1 and flg_w1:
    print('NO')
else:
    print('YES')