C++ :

#include <cstdio>
#include <algorithm>
using namespace std;

const int oo = 2e9;
const int N = 1e5 + 5;

int n;
int x[N], t[N];
int p[N], f[N];
int mx;

bool cmp(int a, int b) {
    if (x[a] != x[b]) return x[a] < x[b];
    return t[a] < t[b];
}

int main() {
    scanf("%d", &n);
    for (int i = 1; i <= n; ++i) {
        scanf("%d%d", &x[i], &t[i]);
        t[i] -= x[i];
        p[i] = i;
        f[i] = oo;
    }
    sort(p + 1, p + n + 1, cmp);
    mx = 0;
    f[0] = 0;
    for (int i = 1; i <= n; ++i) {
        int l = 0, r = mx;
        int v = t[p[i]];
        if (v < 0) continue;
        while (l < r) {
            int mid = (l + r) / 2 + 1;
            if (v < f[mid])
                r = mid - 1;
            else
                l = mid;
        }
        mx = max(mx, r + 1);
        f[r + 1] = v;
    }
    printf("%d\n", mx);
    return 0;
}