#include 

using namespace std;

int broj_na_deliteli(int n, int idx) {
    if(idx > n) {
        return 0;
    }
    bool deliv = ((n % idx) == 0);
    
    return broj_na_deliteli(n, idx + 1) + deliv;
}
int k_deliv(int x, int idx, int k) {
    if(idx < x - k or idx == 0) {
        return 1;
    }
    if(broj_na_deliteli(idx, 1) >= broj_na_deliteli(x, 1)) {
        return 0;
    }
    return k_deliv(x, idx - 1, k);
}
int sum(int a, int b, int k) {
    if(a > b) {
        return 0;
    }
    int dodadi = 0;
    if(k_deliv(a, a - 1, k)) {
        dodadi = a;
    }
    return sum(a + 1, b, k) + dodadi;
}
                              
int main() {
    int a, b, k;
    cin >> a >> b >> k;
    cout << sum(a, b, k) << endl;
    return 0;
}