#include <iostream>

using namespace std;

int main()
{
    int n , m , k , s;

    cin >> n >> m >> k;

    if ((m / 2) * k < 2 * (m / 2) + 10) cout << "0";
    else s = (m + n + k - 1) / k ;
        cout << s;
    return 0;
}