b

#include <iostream>
#include <algorithm>

using namespace std;

int n, d;
int m[10001], s[10001];

inline void Citire()
{
    int i;

    cin >> n >> d;
    for(i = 1; i <= n; ++i)
        cin >> m[i] >> s[i];

}

inline int Solutie()
{
    int i, factor;
    factor =s[1];
    for(i = 2; i <= n; ++i)
    {
        if(m[i] < m[i-1] && m[i-1] - m[i] <= d)
                factor = factor + s[i];
        else if(m[i] >= m[i-1] && m[i] - m[i-1] <= d)
                factor = factor + s[i];
        else if(factor < s[i])
                factor = s[i];
        else if(factor < s[i-1])
            factor = s[i-1];
    }

    sort(s, s+n);

    if(s[n] > factor)
        factor = s[n];
    return factor;
}

int main()
{
    Citire();
    cout << Solutie();

    return 0;
}