Barrel

Some amount of water is poured into a barrel, then several cubes of different size and density are placed into the water. Finally, a lid is put on the barrel and pushed down until it rests on the rim of the barrel.

Write a program that computes the resulting water level in the barrel.

You may assume that:

• the density of water is 1.0,
• the effect of air can be neglected,
• every cube fits completely inside the barrel,
• the cubes do not rotate and do not touch one another.

The first line contains three real numbers: the base area of the barrel $S$ $(0 < S \le 1000)$, the height of the barrel $H$ $(0 < H \le 1000)$, and the volume of water $V$ $(0 < V \le S \cdot H)$.

The second line contains the number of cubes $N$ $(0 < N \le 1000)$.

Each of the following $N$ lines contains two real numbers describing one cube: the side length $L$ $(0 < L \le 1000)$ and the density $D$ $(0 < D \le 10)$.

Print a single line containing the resulting water level, rounded to exactly four decimal places.