#include <bits/stdc++.h>   int freq[1005] = {0};   int find_int(int a, int b, int c, int d) {     int i;     if (b < c) return 0;     if (a > d) return 0;     if (a <= c && b >= d) {       for (i = c; i <= d; i++) freq[i] = 1;       return d - c + 1;     } else if (a >= c && b <= d) {       for (i = a; i <= b; i++) freq[i] = 1;       return b - a + 1;     } else if (a >= c && b >= d) {       for (i = a; i <= d; i++) freq[i] = 1;       return d - a + 1;     } else if (a <= c && b <= d) {       for (i = c; i <= b; i++) freq[i] = 1;       return b - c + 1;     }   }   int main() {     int i, j, k, l, r, p, q, a[55], b[55], c[55], d[55];     scanf( %d %d %d %d , &p, &q, &l, &r);     for (i = 0; i < p; i++) scanf( %d %d , &a[i], &b[i]);     for (i = 0; i < q; i++) scanf( %d %d , &c[i], &d[i]);     int count = 0;     for (i = 0; i < q; i++) {       for (j = 0; j < p; j++) {         int l1, r1;         if (c[i] >= a[j] && c[i] <= b[j]) l1 = 0;         r1 = b[j] - c[i];         if (c[i] < a[j]) {           l1 = a[j] - d[i];           r1 = b[j] - c[i];         }         count = count + find_int(l1, r1, l, r);       }     }     count = 0;     for (i = l; i <= r; i++) {       if (freq[i] == 1) count++;     }     printf( %d n , count);     return 0;   }   