function Main(input) {
	input = input.trim();
  var len = parseInt(input.split("\n")[0]);
  var A = input.split("\n")[1];
  var B = input.split("\n")[2];
  var C = input.split("\n")[3];
  var count = 0;
  if(A == B && B == C){
     console.log(count);
    return;
  }
  for(var i = 0; i < len; i++){
    var tmpA = A.slice(i , i + 1);
    var tmpB = B.slice(i , i + 1);
    var tmpC = C.slice(i , i + 1);
    if(tmpA == tmpB && tmpB == tmpC){
      //console.log("全て同じ(+0)");
      continue;
    }else if(tmpA != tmpB && tmpB != tmpC && tmpA != tmpC){
      //console.log("全て違う(+2)");
       count += 2;
    }else{
      //console.log("その他(+1)");
      count++;
    }
  }
  console.log(count);
}

Main(require("fs").readFileSync("/dev/stdin", "utf8"));
