[Link] https://www.acmicpc.net/problem/2170
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import java.util.*;
import java.io.*;
public class Main {
static BufferedReader br;
// static StringBuilder sb = new StringBuilder();
public static void main(String[] args) throws IOException {
br = new BufferedReader(new InputStreamReader(System.in));
StringBuilder sb = new StringBuilder();
int n = toi(br.readLine());
String[] line;
ArrayList<Line> al = new ArrayList<>();
for(int i = 0; i < n; i++) {
line = br.readLine().split(" ");
long a = Long.parseLong(line[0]), b = Long.parseLong(line[1]);
al.add(new Line(a, b));
}
al.sort((l, r) -> {
if(l.left == r.left) return l.right < r.right ? 1 : -1;
else return l.left > r.left ? 1 : -1;
});
long sl = al.get(0).left, sr = al.get(0).right, totLen = sr - sl;
for(Line ll : al) {
if(sl <= ll.left && ll.right <= sr) continue;
else if(sl == ll.left) {
totLen += ll.right - sr;
} else {
if(sr <= ll.left) {
totLen += ll.right - ll.left;
} else totLen += ll.right - sr;
}
sl = ll.left;
sr = ll.right;
}
print(totLen);
}
static class Line {
long left, right;
Line(long left, long right) { this.left = left; this.right = right; }
}
static int toi(String s) { return Integer.parseInt(s); }
static long tol(String s) { return Long.parseLong(s); }
static String[] getLine() throws IOException { return br.readLine().split(" "); }
static int[] getArr() throws IOException { return Arrays.stream(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray(); }
static <T> void print(T s) { System.out.print(s); }
static <T> void println(T s) { System.out.println(s); }
}