#include <stdio.h>
#include <stdlib.h>
int localdiv(int H, int A)
{
  if (H < 0) H = 0;
  return (H/A + ((H%A)?1:0));
}
int main()
{
  int H;
  int A;
  int D;
  scanf("%d", &H);
  scanf("%d", &A);
  scanf("%d", &D);

  int Hmax = 10000;
  int HdivD = localdiv(H, D);
  int *E = (int*)malloc(sizeof(int)*(HdivD+1));

  int i;
  int min = Hmax*2+1;
  for (i=0; i<=HdivD; i++) {
    E[i] = localdiv(H-D*i, A)*2 + i*3;
    if (E[i] < min) min = E[i];
  }

  if (min%2) {
    printf("%.1f\n", (double)min/2);
  } else {
    printf("%d\n", min/2);
  }
  return 0;
}