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")