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;
}