class Double_Hasher():
    def __init__(self, length, base, mod0, mod1, type=0):
        self.length=length
        self.base=base
        self.mod0=mod0
        self.mod1=mod1
        self.type=type

        self.power0=pw0=[1]*length
        self.power1=pw1=[1]*length
        for i in range(1, length):
            pw0[i]=(base*pw0[i-1])%mod0
            pw1[i]=(base*pw1[i-1])%mod1

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

    def encode(self, S):
        code0=0; code1=0
        N=len(S)
        for i in range(N):
            if self.type:
                code0+=ord(S[i])*self.power0[N-1-i]%self.mod0
                code1+=ord(S[i])*self.power1[N-1-i]%self.mod1
            else:
                code0+=S[i]*self.power0[N-1-i]%self.mod0
                code1+=S[i]*self.power1[N-1-i]%self.mod1

        code0%=self.mod0; code1%=self.mod1
        return code1*self.mod0+code0

#==================================================
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)
    H=Double_Hasher(M,beta,Mod1,Mod2)
    return len(set(H.encode(T[j]) for j in range(N)))==N


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

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