RT,

#include <bits/stdc++.h>
using namespace std;
const int N = 100000;
long long t[N << 2], d[N << 2];
void add(int x, long long v, int L, int R){
	t[x] += (R - L + 1) * v;
	d[x] += v;
	return;
}
void pushup(int x){
	t[x] = t[x << 1] + t[x << 1 | 1];
}
void pushdown(int x, int L, int R){
	if (!d[x]){
		return;
	}
	int mid = (L + R) >> 1;
	add(x << 1, d[x], L, mid);
	add(x << 1 | 1, d[x], mid + 1, R);
	d[x] = 0;
	return;
}
void build(int x, int l, int r){
	if (l == r){
		t[x] = 0;
		return;
	}
	int mid = (l + r) >> 1;
	build(x << 1, l, mid);
	build(x << 1 | 1, mid + 1, r);
	pushup(x);
	return;
}
void change(int x, int l, int r, int v, int L, int R){
	if (l == L && r == R){
		return add(x, v, L, R);
	}
	pushdown(x, L, R);
	int mid = (L + R) >> 1;
	if (r <= mid){
		change(x << 1, l, r, v, L, mid);
	} else if (l > mid){
		change(x << 1 | 1, l, r, v, mid + 1, R);
	} else {
		change(x << 1, l, mid, v, L, mid);
		change(x << 1 | 1, mid + 1, r, v, mid + 1, R);
	}
	pushup(x);
	return;
}
long long query(int x, int l, int r, int L, int R){
	if (l == L && r == R){
		return t[x];
	}
	pushdown(x, L, R);
	int mid = L + R >> 1;
	if (r <= mid){
		return query(x << 1, l, r, L, mid);
	} else if (l > mid){
		return query(x << 1 | 1, l, r, mid + 1, R);
	} else {
		return query(x << 1, l, mid, L, mid) + query(x << 1 | 1, mid + 1, r, mid + 1, R);
	}
}
int main(){
	int n, W, x, b;
	long long ans = 0;
	scanf("%d%d", &n, &W);
	build(1, 1, 100000);
	while (n--){
		scanf("%d%d", &x, &b);
		change(1, x, x, b, 1, 100000);
	}
	for (int i = 1; i <= n - W + 1; i++){
		ans = max(ans, query(1, i, i + W - 1, 1, 100000));
	}
	printf("%lld", ans);
	return 0;
}