import java.util.ArrayList;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        //题意不明，不就是把每一天的历史数量加一起吗
        Scanner scanner = new Scanner(System.in);
        final int nextLineNum = Integer.parseInt(scanner.nextLine());
        ArrayList<Integer> record = new ArrayList<>();
        int toDayHours = hours(scanner.nextLine());
        record.add(toDayHours);
        for (int count = 1; count < nextLineNum; count++) {
//            int yesterdayHour = toDayHours;//难道我这样写？
            toDayHours = toDayHours/*这是前天，试了试用代码太难表达清楚了导致这里变量名还是今天*/ + hours(scanner.nextLine());
            record.add(toDayHours);
        }
        System.out.println(record.stream().mapToInt(Integer::intValue).sum());
    }

    static int hours(String line) {
        String[] two = line.split(" ");
        return Integer.parseInt(two[0]) + Integer.parseInt(two[1]) - 8;
    }
}

入门题都这么难吗？很简单但很难啊