#include<stdio.h>
double fibo(double n);
 
int main(){
  printf("%lf\n", fibo(40));
  printf("\n");
}

double fibo(double n) {
  double f_ant, f_atual, f_aux, cont; 
  cont = 1; 
  f_ant=0; f_atual=1;
  while( cont<=n ){
    f_aux = f_atual;
    f_atual = f_atual + f_ant;
    f_ant = f_aux;
    cont++;
  }
  return f_atual;
}