LAZY C++

#include<bits/stdc++.h>
using namespace std;
int n,k,a[1000000],x,c,i,s=0,maxx=-1,nmax=-1;
void nhap()
{
    cin>>n>>k;
    for(i=1;i<=n;i++)
    {
        cin>>c>>x;
        a[x]=c;
        if(nmax<x) nmax=x;
    }
}
void giai()
{
    for(i=0;i<=2*k;i++)
        s=s+a[i];
    maxx=s;
    for(i=2*k+1;i<=nmax;i++)
    {
        s=s+a[i]-a[i-(2*k+1)];
        if(s>maxx) maxx=s;
    }
    cout<<maxx;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);

    freopen("lazy.inp","r",stdin);
    freopen("lazy.out","w",stdout);
    nhap();
    giai();
}