#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

struct Boxes {
    long long a;
    long long b;
};

bool cmp(Boxes lhs, Boxes rhs) {
    if (lhs.a < lhs.b) {
        if (rhs.a < rhs.b)
            return lhs.a < rhs.a;
        else
            return lhs.a < rhs.b;
    }
    else {
        if (rhs.a < rhs.b)
            return lhs.b < rhs.a;
        else
            return lhs.b < rhs.b;
    }
}

int main() {
    int n;
    long long L;
    cin >> n;
    vector<Boxes> Boxes(n);
    for (int i = 0; i < n; ++i) {
        cin >> Boxes[i].a >> Boxes[i].b;
    }
    cin >> L;

    sort(Boxes.begin(), Boxes.end(), cmp);

    int count = 0;
    int k = 0;
    while (L > 0) {
        if (L - min(Boxes[k].a, Boxes[k].b) < 0) {
            if (min(Boxes[k].a, Boxes[k].b) / 2 >= L) {
                L += min(Boxes[k - 1].a, Boxes[k - 1].b) / 2;
                if (min(Boxes[k].a, Boxes[k].b) / 2 >= L) {
                    break;
                } else {
                    ++count;
                    break;
                }
            }
            else {
                L -= min(Boxes[k].a, Boxes[k].b) / 2;
                ++count;
                ++k;
                if (k == n)
                    break;
            }
        }
        else {
            L -= min(Boxes[k].a, Boxes[k].b);
            ++count;
            ++k;
            if (k == n)
                break;
        }
    }

    if (count == 0)
        count++;

    cout << count;

    return 0;
}