#include<cstdio>


int main(void)
{
	int h, a, d;
	double min, r;

	while(scanf("%d%d%d", &h, &a, &d)==3)
	{
		min=100000.0;
		for(int i=(h+a-1)/a;i>=0;i--)
		{
			if(h-a*i<=0) r=i;
			else r=i+(h-a*i+d-1)/d*1.5;
			if(min>r) min=r;
		}
		printf("%.1f\n", min);
	}

	return 0;
}