#include<stdio.h>
int main() {
    int i, j, a, b;
    int a[100][1000] = 0;
    int count = 0;
    int x, y;
    scanf("%d%d", &i, &j);
    for (x = 0; x < i; x++) {
        for (int y = 0; y <= j; y++) {
            a[x][y] = 1;
        }
    }
    for (x = 0; x < i; x++) {
        scanf("%d%d", &a, &b);
        for (int y = a; y <= b; x++) {
            a[x][y] = 0;
        }
    }
    for (x = 0; x < i;) {
        for (int y = 0; y <= j; y++)
            count = count + a[y][x];
    }
    printf("%d", count);
    return 0;
}