#include <bits/stdc++.h>
using namespace std;
const int N = 500007;
int dis[N], num[N], f[N], que[N];
int n, d, k, l, r, ans = 0;

int check(int val)
{
    memset(f, -127, sizeof(f));
    int head = 1, tail = 0, mi = val < d ? d - val : 1, mx = d + val, ret = 0, fir = -1;
    que[++tail] = 0, f[0] = 0; 
    for (int i = 1; i <= n; i++)
    {
        if (dis[i] < mi) continue;
        if (dis[i] >= mi && fir == -1) 
            fir = i;
        if (dis[i] - dis[i - 1] > mx) break; 
        while (dis[i] - dis[fir] >= mi && fir < i) 
        {
            while (head <= tail && f[fir] > f[que[tail]]) tail--; 
            que[++tail] = fir++; 
        }
        while (head <= tail && dis[que[head]] + mx < dis[i]) head++; 
        if (head > tail) 
            f[i] = -0x7f7f7f7f; 
        else
            f[i] = f[que[head]] + num[i]; 
        if (f[i] > ret) 
            ret = f[i];
    }
    return ret >= k; 
}

int main()
{
    //freopen("jump.in","r",stdin);
    //freopen("jump.out","w",stdout);
    cin>>n>>d>>k;
    for (int i = 1; i <= n; i++)
       cin>>dis[i]>>num[i];
    l = 0, r = dis[n];
    while (l <= r) 
    {
        int mid = (l + r) / 2;
        if (check(mid)) 
            r = mid - 1, ans = mid;
        else
            l = mid + 1;
    }
    if (check(ans)) 
        cout << ans;
    else
        cout << -1;
    return 0;
}