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

    H1=[0]*N; Mod1=10**9+7
    H2=[0]*N; Mod2=10**9+9
    beta=randint(2,Mod1-1)

    for i in range(M):
        S=input()
        for j in range(N):
            s=int(S[j])
            H1[j]=(beta*H1[j]+s)%Mod1
            H2[j]=(beta*H2[j]+s)%Mod2

    H=[H1[j]*Mod2+H2[j] for j in range(N)]
    return len(set(H))==N

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

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