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

using namespace std;

double other_leg(const double leg, const double diag) {
    return sqrt(diag * diag - leg * leg);
}

double diag(const double leg1, const double leg2) {
    return sqrt(leg1 * leg1 + leg2 * leg2);
}

vector<pair<double, double>> target_ranges(vector<pair<int, int>> islands, const int distance) {
    vector<pair<double, double>> ranges;
    for (auto& [island_x, island_y] : islands) {
        if (island_y > distance) { throw std::runtime_error("Island is too far away from the radar."); }
        const double offset = other_leg(island_y, distance);
        ranges.emplace_back(island_x - offset, island_x + offset);
    }
    sort(ranges.begin(), ranges.end(),
         [](const auto& a, const auto& b) { return a.second < b.second; });
    return ranges;
}

int required_radars(const vector<pair<double, double>>& ranges) {
    if (ranges.empty()) { return 0; }
    int answer = 1;
    double current_max_x = ranges[0].second;
    for (const auto& [left,right] : ranges) {
        if (left > current_max_x) { answer++, current_max_x = right; } // 放不下，加雷达
        else if (right < current_max_x) { current_max_x = right; } // 放下，需要左移雷达
        clog << "current_max_x: " << current_max_x << " answer: " << answer << endl;
    }
    return answer;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, distance, case_id = 0;
    while (cin >> n >> distance) {
        if (n == 0 && distance == 0) { break; }
        vector<pair<int, int>> islands(n);
        for (int i = 0; i < n; i++) {
            cin >> islands[i].first >> islands[i].second;
        }
        // cout << "Case " << ++case_id << ": ";
        try {
            cout << required_radars(target_ranges(islands, distance)) << endl;
        } catch (std::runtime_error&) {
            cout << -1 << endl;
        }
    }
}