#include <stdio.h>

int main()
{
  int n, i, a=1, b=2, c;

  scanf("%d", &n);

  for (i=3; i<=n; i++) {
    c = a+b;
    a = b;
    b = c;
  }

  printf("F_%d = %d\n", n, c);

  return 0;
}