ЦЕПЬ (Областная олимпиада 2019, день 1)

#include <bits/stdc++.h>

using namespace std;

int main(){
    int m, k, ans = 0;
    cin >> m >> k;

    if (k == 1) {
        for (int l = 1; l <= m; l++) {
            for (int r = l; r <= m; r++) {
                ans++;
            }
        }
        ans--;
    }

    if (k == 2) {
        for (int l1 = 1; l1 <= m; l1++) {
            for (int r1 = l1; r1 <= m; r1++) {
                for (int l2 = r1 + 2; l2 <= m; l2++) {
                    for (int r2 = l2; r2 <= m; r2++) {
                        ans++;
                    }
                }
            }
        }
    }

    if (k == 3) {
        for (int l1 = 1; l1 <= m; l1++) {
            for (int r1 = l1; r1 <= m; r1++) {
                for (int l2 = r1 + 2; l2 <= m; l2++) {
                    for (int r2 = l2; r2 <= m; r2++) {
                        for (int l3 = r2 + 2; l3 <= m; l3++) {
                            for (int r3 = l3; r3 <= m; r3++) {
                                ans++;
                            }
                        }
                    }
                }
            }
        }
    }

    cout << ans % 1000 << endl;
}