|Input file:||input.txt||Time limit:||1 sec|
|Output file:||output.txt||Memory limit:||256 Mb|
Wilhelm plays Gorn game in virtual reality, fighting against N gladiators on the arena. He has a bow and an infinite number of arrows and never misses an enemy with a shot.
When Wilhelm hits an enemy gladiator for the first time, he inflicts D points of damage, so gladiator loses D hit points. Every following hit on the same gladiator increases damage by K points due to weakening of the gladiator's armor. When hitting a new gladiator, damage again starts with D and increases after each hit. Gladiator dies when his hit points become zero or negative.
What is the minimum number of arrows Wilhelm must spend to kill all gladiators?
1 ≤ N ≤ 104
1 ≤ D ≤ 105
1 ≤ K ≤ 103
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