#include<bits/stdc++.h>
using namespace std;
const int N=1e6+10;
long long f[N],x[N],s[N],n,d,k;
bool check(int g){
    long long pos;
    memset(f,0,sizeof f);
    deque<int>q;
    long long l=max((long long)1,d-g),r=d+g;
    for(int i=1;i<=n;i++){
        while(x[pos]+l<=x[i]){
            while(!q.empty() && f[q.back()]<f[pos]){
                q.pop_back();
            }
            q.push_back(pos);
            pos++;
        }
        while(!q.empty() && x[q.front()]+r<x[i]){
            q.pop_front();
        }
        if(!q.empty()){
            f[i]=f[q.front()]+s[i];
        }else{
            f[i]=-1e18;
        }
        if(f[i]>=k){
            return 1;
        }
    }
    return 0;
}
int main(){

    cin>>n>>d>>k;
    for(int i=1;i<=n;++i){
        cin>>x[i]>>s[i];
    }
    int L=1,R=x[n];
    while(L<=R){
        int mid=(L+R)/2;
        if(check(mid)){
            R=mid;
        }else{
            L=mid+1;
        }
    }
    if(L==x[n]){
        cout<<-1;
    }else{
        cout<<L;
    }
    return 0;
}