D15.4 喝汽水，1瓶汽水1元，2个空瓶可以换一瓶汽水， 给20元，可以多少汽水。 编程实现。

#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>

int main()
{
	int cover;
	int sum;
	int n;
	scanf("%d%d", &cover, &n);
	sum = cover;

	while (cover >= n)
	{
		sum += cover / n;
		cover = cover / n + cover%n;

	}
	printf("%d", sum + (cover == n - 1));
	system("pause");
	return 0;

}