function Main(input) {
  input = input.split("\n");
  var n = parseInt(input[0].split(" ")[0]);
  w = new Array(n).fill(0);
  var ans = "Yes";
  for(i=0;i<n;i++){
    w[i]=input[i+1];
    if(i>0){
      if(w[i].substr(0,1)!=w[i-1].substr(w[i-1].length-1,1)){
        ans="No";
        break;
      }
    }
    for(j=0;j<i;j++){
      if(w[i]==w[j]){
        ans="No";
        break;
      }
    }
  }


  console.log('%s', ans);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));