#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;

int main() {
  int N;
  double d, x;

  scanf("%d%lf%lf", &N, &d, &x);

  double res = 0;

  while (N) {
    res += d + (N - 0.5) * x;
    d += d / N + 5 * x / 2.0 / N;
    x += 2 * x / N;
    N--;
  }

  printf("%.10lf\n", res);
  return 0;
}
