#include <iostream>
using namespace std;

int main()
{
    int n, m, k;
    cin >> n >> m >> k;

    int ch = n / (k-2), pa = m / 2, all = (n + m) / k;
    int ch2 = n % (k-2), ost = (n+m) % k;
    if(ch2 == 0)
        if(ch > pa)
            cout << 0;
        else
            if(ost == 0)
                cout << all;
            else
                cout << all + 1;
    else
        if(ch + 1 > pa)
            cout << 0;
        else
            if(ost == 0)
                cout << all;
            else
                cout << all + 1;

    return 0;
}