// (define (fib n)
//   (f n 0 0 1))
// 
// (define (f n i fi fi1)
//   (if (= i n)
//       fi
//       (f n (+ i 1) fi1 (+ fi fi1))))

public class fib2 {
    public static void main(String [] args) {
        System.out.println(fib(Integer.parseInt(args[0])));
    }
    
    public static double fib(int n) {
        return f(n,0,0,1);
    }

    private static double f(int n, int i, double fi, double fi1) {
        
        while (i!=n) {
            double old_fi = fi;
            i = i+1;
            fi = fi1;
            fi1 = old_fi+fi1;
        }
        return fi;
    }

}