C++ :

#include <bits/stdc++.h>
using namespace std;
 
const int Max=500005;
int n,m,k,d,head,tail,l,r,mid,maxlen,minlen,now,tag;
int x[Max],num[Max],f[Max],p[Max];
 
inline int get_int()
{
	int x=0,f=1;
	char c;
	for(c=getchar();(!isdigit(c))&&(c!='-');c=getchar());
	if(c=='-') f=-1,c=getchar();
	for(;isdigit(c);c=getchar()) x=(x<<3)+(x<<1)+c-'0';
	return x*f;
}
 
inline bool check(int len)
{
	now=0,head=1,tail=0,maxlen=len+d,minlen=max(d-len,1);
	for(int i=1;i<=n;i++)
	{
	  while(x[now]<=x[i]-minlen)
	  {
	    if(f[now]<=-1e9) {now++;continue;}   //不能到达now 
	    while(head<=tail&&f[now]>=f[p[tail]]) tail--;
	    p[++tail]=now,now++;   //放进队列 
	  }
	  while(head<=tail&&x[p[head]]<x[i]-maxlen) head++;
	  if(head<=tail) f[i]=f[p[head]]+num[i];
	  else f[i]=-1e9;
	  if(f[i]>=k) return 1;  //有满足的直接返回 
	}
	return 0;
}
 
int main()
{
	n=get_int(),d=get_int(),k=get_int();
	for(int i=1;i<=n;i++) x[i]=get_int(),num[i]=get_int();
	l=0,r=500000;
	while(l<r)  //二分答案 
	{
	  mid=(l+r)>>1;
	  if(check(mid)) tag=1,r=mid;
	  else l=mid+1;
	}
	if(tag) cout<<r;
	else cout<<"-1\n";
	return 0;
}