#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

using namespace std;

typedef long long ll;

int const xn=5e5+;

int n,d,k,x[xn],s[xn],q[xn],h,t;

ll f[xn],inf=1e17;

int rd()

{

  int ret=,f=; char ch=getchar();

  while(ch<''||ch>''){if(ch=='-')f=; ch=getchar();}

  while(ch>=''&&ch<='')ret=(ret<<)+(ret<<)+ch-'',ch=getchar();

  return f?ret:-ret;

}

void add(int x)

{

  while(h<=t&&f[q[t]]<=f[x])t--;

  q[++t]=x;

}

bool ck(int g)

{

  h=,t=; int mn=max(d-g,);

  memset(f,-,sizeof f);

  x[]=; q[]=-; f[]=;

  for(int i=;i<=n;i++)

    {

      while(x[i]-x[q[t]+]>=mn)add(q[t]+);//

      while(h<=t&&x[i]-x[q[h]]>d+g)h++;

      if(h<=t)f[i]=f[q[h]]+s[i];

      if(f[i]>=k)return ;

    }

  return ;

}

int main()

{

  n=rd(); d=rd(); k=rd();

  for(int i=;i<=n;i++)x[i]=rd(),s[i]=rd();

  int l=,r=max(x[n]-d,d-),ans=-;

  while(l<=r)

    {

      int mid=((l+r)>>);

      if(ck(mid))ans=mid,r=mid-;

      else l=mid+;

    }

  printf("%d\n",ans);

  return ;

}