C++ :

#include<iostream>
#include<cstdio>
using namespace std;
struct Region {
    double s, e;
}r1[101], r2[101];
double min(double a, double b) { return a < b ? a : b; }
double max(double a, double b) { return a > b ? a : b; }
double cal(Region a, Region b) { // a是靠前的区间
    double dif;
    char first;
    if (a.e < b.e) dif = a.e - max(a.s, b.s), first = 'a';
    else dif = b.e - max(a.s, b.s), first = 'b';
    if (dif > 0) {
        if (first == 'a') a.s = a.e, b.s = b.e;
        else a.s = b.e, b.s = b.e;
        return dif;
    }
    else return 0;
}
int main() {
    int n1, n2;
    while (cin >> n1) {
        for (int i = 0; i < n1; i++) cin >> r1[i].s >> r1[i].e;
        cin >> n2;
        for (int i = 0; i < n2; i++) cin >> r2[i].s >> r2[i].e;
        double ans = 0;
        for (int i = 0; i < n1; i++) for (int j = 0; j < n2; j++) {
            if (r1[i].s < r2[j].s) ans += cal(r1[i], r2[j]);
            else ans += cal(r2[j], r1[i]);
        }
        printf("%.3lf\n", ans);
    }
    return 0;
}