#include <iostream>

using namespace std;

int main()
{
    int n, d, t;
    int k = 1;
    int cur = 0;
    cin >> n >> d >> t;
    for (int i = 0; i < n; i++) {
        int x, y;
        cin >> x >> y;
        while (cur < x) {
            cur += 20;
            k += 1;
        }
        if (cur < y && cur > x) {
            cur = x;
        }
    }
    while (cur < t) {
        cur += 20;
        k += 1;
    }
    cout << k << endl;
}