class Fibonacci{
    public static int fib(int n){
        int prev = 0 ; 
        int fib  = 1 ;
        for(int i = 1 ; i < n; i++) {
            int next = prev + fib ;
            prev     = fib  ;
            fib      = next ;
        }
        return fib; // fib = fib(n)
    }
}