// luogu-judger-enable-o2
#include<cstdio>
#include<algorithm>
#include<iostream>
using namespace std;
struct node
{
    int tree[100100];
    int num;
    int lowbit(int x)
    {
        return x&(-x);
    }
    void updata(int x,int i)
    {
        while(i<=num)
        {
            tree[i]+=x;
            i+=lowbit(i);
        }
    }
    int sum(int i)
    {
        int ans=0;
        while(i>0)
        {
            ans+=tree[i];
            i-=lowbit(i);
        }
        return ans;
    }
    int check(int l,int r)
    {
        return sum(r)-sum(l-1);
    }
};
node bit;
int main()
{
    int n,m;
    scanf("%d%d",&n,&m);
    bit.num=n;
    int a,b;
    for(int i=1;i<=n;i++)
    {
        scanf("%d%d",&a,&b);
        bit.updata(b,a);
    }
    int ans=0;
    for(int i=1;i+m-1<=n;i++)
        ans=max(ans,bit.check(i,i+m-1));
    printf("%d",ans);
}