function main(input) {
  const args = input.split('\n');
  const N = parseInt(args[0], 10);
  const A = args[1].split("");
  const B = args[2].split("")
  const C = args[3].split("")
  var count = 0
  
  for(var i = 0; i<N; i++){
    count += add(A[i],B[i],C[i])
  }
  console.log(count)
}

function add (a,b,c){
  if(a == b && b == c){
    return 0
  }else if(a == b || b == c || c == a){
    return 1
  }else{
    return 2
  }
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));