function main(input) {
  input = input.split("\n");
  var n = input[0];
  var A = input[1];
  var B = input[2];
  var C = input[3];
  var count = 0;
  for (var i = 0; i < n; i++) {
    if (!(A[i] === B[i] && B[i] === C[i]))
      if (A[i] === B[i] || B[i] === C[i] || C[i] === A[i])
        count++;
      else
        count += 2;
  }
  console.log(count);
}
main(require("fs").readFileSync("/dev/stdin", "utf8"));