import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] sa = br.readLine().split(" ");
		int a = Integer.parseInt(sa[0]);
		int b = Integer.parseInt(sa[1]);
		int s = Integer.parseInt(sa[2]);
		br.close();

		long ans = 0;
		for (int x = 1; x <= a; x++) {
			int ym = Math.min(s / x, b);
			long v1 = a - x + 1;
			long v21 = (long) b * (b + 1) / 2;
			long r = b - ym;
			long v22 = r * (r + 1) / 2;
			long val = v1 * (v21 - v22);
			ans += val;
		}
		System.out.println(ans);
	}
}