Please do this task, for you is probably easy but I'm stupid ...
Thanks to everyone who help me.
Waterpolo player Jimmy participate in preparations for the competition for a period of N days. The first day of preparation Jimmy swim a meter, and every next day for D meters more than the previous day. Write a program that determines how much Jimmy meters swim on the last day of preparation.
Enters
the three integers, each in a separate line of standard input. Numbers respectively represent the number of days that the preparation last N
(N≤20), how many meters Jimmy swim first day of the preparation of A (a≤3000), how many meter every day Jimmy more floats in relation to previous day D (d≤1000)
Exit
In the standard output display how many meters Jimmy swim on the last day of preparation
Example
entrance
10
500
100
Exit
1400