#include <bits/stdc++.h>

long double f(long double p, long double pp) {
  return (19 * p - 12 * pp) / 4;
}

int main() {
  long double memo[128] = {};
  memo[0] = 4;
  memo[1] = 3;
  // for(int i = 2; i <= 100; ++i) {
  //   printf("%3d : %.20lf\n", i, (double)(memo[i] = f(memo[i-1], memo[i-2])));
  // }

  long double diff[128]; // diff[i] = ax[i] - 4 * ax[i-1] => ax[i] = diff[i] + 4 * ax[i-1]
  diff[1] = -13;
  for(int i = 2; i < 128; ++i) {
    diff[i] = diff[i-1] * 3 / 4;
  }
  // for(int i = 1; i <= 100; ++i) {
  //   printf("%lf %lf\n", (double)(memo[i] - 4 * memo[i-1]), (double)diff[i]);
  // }

  for(int i = 2; i < 128; ++i) {
    memo[i] = diff[i] + 4 * memo[i-1];
  }
  for(int i = 2; i < 128; ++i) {
    memo[i] = memo[i-1] * 3 / 4;
  }
  // for(int i = 2; i <= 100; ++i) {
  //   printf("%3d : %.20lf\n", i, (double)(memo[i]));
  // }
  int n;
  scanf("%d", &n);
  printf("%.30lf\n", (double)memo[n]);

  return 0;
}