text: /*
   * Author        : OFShare
   * E-mail        : OFShare@outlook.com
   * Created Time  : 2020-02-19 15:59:10 PM
   * File Name     : P1720.cc
   */
  
  #include <bits/stdc++.h>
  
  void debug() {
    #ifdef Acui
      freopen("data.in", "r", stdin);
      freopen("data.out", "w", stdout);
    #endif
  }
  
  int n;
  int main() {
    scanf("%d", &n);
    if (n == 0) printf("0.00\n");
    else if (n == 1) printf("1.00\n");
    else {
      double a = 0, b = 1;
      for (int i = 2; ; ++i) {
        double c = a + b;
        if (i == n) {
          printf("%.2lf\n", c * 1.0);
          break;
        }
        a = b;
        b = c;
      }
    }
    return 0;
  }
  