public class Main {

	static final int N = 1000000;
	static final int SIZE = N * 10;
	static byte[] buf = new byte[SIZE];
	static int count = 0;

	static int readInt(){

		while((buf[count] < '0' || '9' < buf[count]) && (buf[count] != '-')){
			count++;
		}

		int r = 0;
		boolean minusFlg = false;
		while(buf[count] == '-'){
			minusFlg = true;
			count++;
		}
		while('0' <= buf[count] && buf[count] <= '9'){
			r = r * 10 + buf[count++] - '0';
		}
		if(minusFlg){
			r = -1 * r;
		}

		if((char)buf[count] == '\r' && (char)buf[count + 1] == '\n'){
			count += 2;
		}else if((char)buf[count] == '\n' || (char)buf[count] == '\r'){
			count++;
		}

		return r;

	}

	static long readLong(){

		while((buf[count] < '0' || '9' < buf[count]) && (buf[count] != '-')){
			count++;
		}

		long r = 0;
		boolean minusFlg = false;
		while(buf[count] == '-'){
			minusFlg = true;
			count++;
		}
		while('0' <= buf[count] && buf[count] <= '9'){
			r = r * 10 + buf[count++] - '0';
		}
		if(minusFlg){
			r = -1 * r;
		}

		if((char)buf[count] == '\r' && (char)buf[count + 1] == '\n'){
			count += 2;
		}else if((char)buf[count] == '\n' || (char)buf[count] == '\r'){
			count++;
		}

		return r;

	}

	static String readStr(){

		String r = "";

		while(buf[count] < '!' || '~' < buf[count]){
			count++;
		}

		while('!' <= buf[count] && buf[count] <= '~'){
			r = r + (char)buf[count++];
		}

		if((char)buf[count] == '\r' && (char)buf[count + 1] == '\n'){
			count += 2;
		}else if((char)buf[count] == '\n' || (char)buf[count] == '\r'){
			count++;
		}

		return r;

	}

	static String readStrContainBlank(){

		String r = "";

		while(buf[count] < ' ' || '~' < buf[count]){
			count++;
		}

		while(' ' <= buf[count] && buf[count] <= '~'){
			r = r + (char)buf[count++];
		}

		if((char)buf[count] == '\r' && (char)buf[count + 1] == '\n'){
			count += 2;
		}else if((char)buf[count] == '\n' || (char)buf[count] == '\r'){
			count++;
		}

		return r;

	}

	static char readChar(){

		char r;

		while(buf[count] < '!' || '~' < buf[count]){
			count++;
		}

		r = (char)buf[count++];

		if((char)buf[count] == '\r' && (char)buf[count + 1] == '\n'){
			count += 2;
		}else if((char)buf[count] == '\n' || (char)buf[count] == '\r'){
			count++;
		}

		return r;

	}

	static char readCharOneContainBlank(){

		char r;

		while(buf[count] < ' ' || '~' < buf[count]){
			count++;
		}

		r = (char)buf[count++];

		if((char)buf[count] == '\r' && (char)buf[count + 1] == '\n'){
			count += 2;
		}else if((char)buf[count] == '\n' || (char)buf[count] == '\r'){
			count++;
		}

		return r;

	}

	static String readLine(){

		String r = "";

		while('\n' != (char)buf[count] && '\r' != (char)buf[count]){
			r = r + (char)buf[count++];
		}

		if((char)buf[count] == '\r' && (char)buf[count + 1] == '\n'){
			count += 2;
		}else if((char)buf[count] == '\n' || (char)buf[count] == '\r'){
			count++;
		}

		return r;

	}

	public static void main (String[] args) throws Exception {

		// 読込
		System.in.read(buf,0,SIZE);

		int n = readInt();
		String a = readLine();
		String b = readLine();
		String c = readLine();

		char[] charA = a.toCharArray();
		char[] charB = b.toCharArray();
		char[] charC = c.toCharArray();

		int operation = 0;
		for(int i = 0; i < n; i++) {
			//全部同じ文字
			if(charA[i] == charB[i] && charA[i] == charC[i]) {
				continue;
			}

			//Aだけ違う文字
			if(charB[i] == charC[i] && charA[i] != charB[i]) {
				operation++;
				continue;
			}

			//Bだけ違う文字
			if(charA[i] == charC[i] && charA[i] != charB[i]) {
				operation++;
				continue;
			}

			//Cだけ違う文字
			if(charA[i] == charB[i] && charA[i] != charC[i]) {
				operation++;
				continue;
			}

			operation += 2;
		}

		System.out.println(operation);

	}

}


Measured memory_bytes: 33232