#include <cstdio>
#include <algorithm>
using namespace std;
struct segmenttree {
    int a[100010];
    int maxv[400010], lazy[400010];
    void pushup(int p) {
        maxv[p] = max(maxv[p << 1], maxv[p << 1 | 1]);
    }
    void pushtag(int p, int x) {
        maxv[p] += x;
        lazy[p] += x;
    }
    void pushdown(int p) {
        if (lazy[p]) {
            pushtag(p << 1, lazy[p]);
            pushtag(p << 1 | 1, lazy[p]);
            lazy[p] = 0;
        }
    }
    void build(int p, int l, int r) {
        if (l == r) {
            maxv[p] = a[l];
            return;
        }
        int mid = (l + r) >> 1;
        build(p << 1, l, mid);
        build(p << 1 | 1, mid + 1, r);
        pushup(p);
    }
    void modify(int p, int l, int r, int L, int R, int x) {
        if (L <= l && r <= R) {
            pushtag(p, x);
            return;
        }
        pushdown(p);
        int mid = (l + r) >> 1;
        if (L <= mid) {
            modify(p << 1, l, mid, L, R, x);
        }
        if (R > mid) {
            modify(p << 1 | 1, mid + 1, r, L, R, x);
        }
        pushup(p);
    }
    int query(int p, int l, int r, int L, int R) {
        if (L <= l && r <= R) {
            return maxv[p];
        }
        pushdown(p);
        int mid = (l + r) >> 1, ans = 0;
        if (L <= mid) {
            ans = max(ans, query(p, l, mid, L, R));
        }
        if (R > mid) {
            ans = max(ans, query(p, mid + 1, r, L, R));
        }
        return ans;
    }
} sgt;
struct node {
    int l, r;
} x[100010];
bool cmp(node a, node b) {
    return a.l < b.l;
}
int n, m;
int main() {
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= n; i++) {
        scanf("%d%d", &x[i].l, &x[i].r);
        x[i].r = m - x[i].r + 1;
    }
    sort(x + 1, x + n + 1, cmp);
    for (int i = 1; i <= m; i++) {
        sgt.a[i] = -i;
    }
    sgt.build(1, 0, m);
    int ans = 0;
    for (int i = 1; i <= n; i++) {
        sgt.modify(1, 0, m, x[i].r, m, 1);
        ans = max(ans, sgt.query(1, 0, m, 0, m) - x[i].l);
    }
    printf("%d\n", ans);
    return 0;
}