Expedition    exp.X

A group of cows grabbed a truck and ventured on an expedition deep into the
jungle. Being rather poor drivers, the cows unfortunately managed to run
over a rock and puncture the truck's fuel tank. The truck now leaks one
unit of fuel every unit of distance it travels.

To repair the truck, the cows need to drive to the nearest town (no more
than 10,000,000 units distant) down a long, winding road. On this road,
between the town and the current location of the truck, there are N (1 <= N
<= 50,000) fuel stops where the cows can stop to acquire additional fuel.
The i-th fuel stop is a distance of D_i (1 <= D_i < L) from the town, and
contains F_i (1 <= F_i <= 100) fuel.

The jungle is a dangerous place for humans and is especially dangerous for
cows. Therefore, the cows want to make the minimum possible number of stops
for fuel on the way to the town. Fortunately, the capacity of the fuel tank
on their truck is so large that there is effectively no limit to the amount
of fuel it can hold. The truck is currently L units away from the town and
has P units of fuel (1 <= P <= 10,000,000).

Determine the minimum number of stops needed to reach the town, or if the
cows cannot reach the town at all. Note that it is possible for there to be
multiple fuel stops at the same location, but they should be counted
separately in the total number of stops.

PROBLEM NAME: exp.X

INPUT FORMAT:

* Line 1: Three space-separated integers: N, L, and P.

* Lines 2..N+1: Line i+1 contains the two integers D_i and F_i.

SAMPLE INPUT:

4 25 10
4 4
5 2
11 5
15 10

INPUT DETAILS:

The truck is 25 units away from the town; the truck has 10 units of fuel. 
Along the road, there are 4 fuel stops at distances 4, 5, 11, and 15 from
the town (so these are initially at distances 21, 20, 14, and 10 from the
truck).  These fuel stops can supply up to 4, 2, 5, and 10 units of fuel,
respectively.

OUTPUT FORMAT:

* Line 1: A single integer giving the minimum number of fuel stops
        necessary to reach the town.  If it is not possible to reach
        the town, output -1.

SAMPLE OUTPUT:

2

OUTPUT DETAILS:

Drive 10 units, stop to acquire 10 more units of fuel, drive 4 more units,
stop to acquire 5 more units of fuel, then drive to the town.