// parameter "input" gets all data
function Main(input) {
	// the first line is assigned to input[0], the second line is assigned to input[1] similarly.
	var splitInput = input.split("\n");
	var n = (splitInput[0])
	var a = (splitInput[1])
	var b = (splitInput[2])
	var c = (splitInput[3])
	
	var result = 0
	
	for (var i=0; i<n; i++){
		if (a[i] == b[i] && a[i] == c[i]) {
			result += 0
		} else if (a[i] == b[i] || a[i] == c[i] || c[i] == b[i]) {
			result += 1
		} else {
			result += 2
		}
	}
	
	//output
	console.log('%d',result);
}
// Don't edit this line!
Main(require("fs").readFileSync("/dev/stdin", "utf8"));