function diff(a,b,c) {
	if (a === b && b === c) {
		return 0
	}

	if (a === b || b === c || c === a) {
		return 1
	}

	return 2
}


function main(arg) {
	var tmp = arg.split("\n")
	var N = Number(tmp[0])
	var A = tmp[1]
	var B = tmp[2]
	var C = tmp[3]

	var sum = 0

	for (var i = 0; i < N;i ++) {
		var tmp = diff(A[i], B[i], C[i])
		sum += tmp
	}

	console.log(sum)
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));