#include <bits/stdc++.h>
using namespace std;
 
int main() {
	int N, M, i, j;
	char c;
	scanf("%d%d", &N, &M);
	string S[N];
	for(i = 0; i < N; ++i){
		S[i] = "";
	}
	for(i = 0; i < M; ++i){
		for(j = 0;j < N; ++j){
			scanf(" %c ", &c);
			S[j] += c;
		}
	}
	sort(S, S + N);
	for(i = 0;i < N - 1; ++i){
		if(S[i] == S[i + 1]){
			printf("No\n");
			return 0;
		}
	}
	printf("Yes\n");
}