#include <bits/stdc++.h>
const int N = 510;

using namespace std;
int n, m, ans;

int f[N][N];

struct Node {
    int x, y;
    const bool operator<(const Node &t) const {
        if (x == t.x) return y < t.y;
        return x < t.x;
    }
} a[N];

int dfs(int u, int r) {
    if (f[u][r]) return f[u][r];
    int ans = r + 1;

    for (int i = u + 1; i <= n; i++) {
        if (a[i].y < a[u].y) continue;
        int d = a[i].x - a[u].x + a[i].y - a[u].y - 1;
        if (d > r) continue;
        ans = max(ans, dfs(i, r - d) + d + 1);
    }
    return f[u][r] = ans;
}

int main() {
    cin >> n >> m;
    for (int i = 1; i <= n; i++) cin >> a[i].x >> a[i].y;
    sort(a + 1, a + 1 + n);

    for (int i = 1; i <= n; i++) ans = max(ans, dfs(i, m));
    printf("%d\n", ans);
    return 0;
}