You are given an integer number n. The following algorithm is applied to it:

  1. if n = 0, then end algorithm; 
  2. find the smallest prime divisor d of n; 
  3. subtract d from n and go to step 1. 



Determine the number of subtrations the algorithm will make.

Input

The only line contains a single integer n (2 ≤ n ≤ 10^{10}).

Output

Print a single integer — the number of subtractions the algorithm will make.

Examples

Input


5


Output


1


Input


4


Output


2

Note

In the first example 5 is the smallest prime divisor, thus it gets subtracted right away to make a 0.

In the second example 2 is the smallest prime divisor at both steps.
function solve(n) {
    var steps = 0;
    var square = Math.sqrt(n);
    var smallestDivisor = n;
    
    while (n !== 0) {
        if (n % 2 === 0) {
            smallestDivisor = 2;
            return steps + n / 2;
        }
        
        var d = 3;
        while (d < Math.min(square, smallestDivisor)) {
            if (n % d === 0) {
                smallestDivisor = d;
                break;
            }
            d += 2;
        }

        n -= smallestDivisor;
        steps++;
    }

    return steps;
}

var number = +readline()
write(solve(number))