#include <stdio.h>

int main(void){

  int n;
  int fib,last=1,before_last=0;
  int i;

  printf("Enter a positive integer\n");
  scanf("%d",n);

  for (i=2; i<n ; i++){
    fib=last+before_last;
    before_last=last;
    last=fib;
  }

  printf("F[%d]=%d\n",n,fib);
}