def solve():
    from random import randint
    N=int(input())
    M=int(input())

    H=[0]*N; Mod1=10**9+7
    beta=randint(2,Mod1-1)

    for i in range(M):
        S=input()
        for j in range(N):
            s=int(S[j])
            H[j]=(beta*H[j]+s)%Mod1
    return len(set(H))==N

#==================================================
import sys
input=sys.stdin.readline
write=sys.stdout.write

print("Yes" if solve() else "No")