class Hasher():
    def __init__(self, length, base, mod, type=0):
        self.length=length
        self.base=base
        self.mod=mod
        self.type=type

        self.power=pw=[1]*length
        for i in range(1, length):
            pw[i]=(base*pw[i-1])%mod

    def __repr__(self):
        return "length: {}\nbase: {}\nmod: {}".format(self.length, self.base, self.mod)

    def encode(self, S):
        code=0; N=len(S)
        for i in range(N):
            if self.type:
                code+=ord(S[i])*self.power[N-1-i]%self.mod
            else:
                code+=S[i]*self.power[N-1-i]%self.mod

        return code%self.mod

    def decode(self, S):
        pass

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

    T=[[0]*M for _ in range(N)]
    for i in range(M):
        S=input()
        for j in range(N):
            T[j][i]=int(S[j])

    E=set()
    Mod1=10**9+7; Mod2=10**9+9
    beta=randint(2,Mod1)
    H1=Hasher(M,beta,Mod1,0)
    H2=Hasher(M,beta,Mod2,0)

    for j in range(N):
        ha=H1.encode(T[j])*Mod2+H2.encode(T[j])
        if ha in E:
            return False
        E.add(ha)
    return True


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

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