#include <cstdio>
#include <vector>
#include <algorithm>

int main() {
  size_t k;
  scanf("%zu", &k);

  std::vector<double> e(k);
  e[0] = 1;
  for (size_t i = k-1; i > 0; --i) {
    for (size_t j = 1; j <= 6; ++j) {
      if (i-j < e.size()) {
        e[i-j] += (1 + e[i]) / 6.0;
      }
    }
  }
  printf("%.12f\n", e[0]);
}