Количество троек

#include <bits/stdc++.h>
#define ll long long
#define pb push_back

using namespace std;

int main() {
    int l1, r1, l2, r2, l3, r3;
    cin >> l1 >> r1 >> l2 >> r2 >> l3 >> r3;

    const int maxn = 2e6 + 3;

    ll cnt[maxn] = {};

    // l1 <= i <= r1   =>  l2 <= j <= r2    l3 <= k <= r3,   k % j == 0  && j % i == 0

    for (int i = l1; i <= r1; ++i) {
        for (int j = i; j < maxn; j += i) {
            cnt[j]++;
        }
    }

    ll ans = 0;

    for (int j = l2; j <= r2; ++j) {
        ans += cnt[j] * (r3 / j - (l3 - 1) / j);
    }

    cout << ans;
    return 0;
}


/*
2 6
1 8
8 10



l1 = 2, r1 = 6
i = 3
j = 3; += 3

i = 2 => 2, 4,  6,  8
i = 3 => 3, 6
i = 4 => 4, 8
i = 5 => 5
i = 6 => 6


cnt[0] = 0
cnt[1] = 0
cnt[2] = 1
cnt[3] = 1
cnt[4] = 2
cnt[5] = 1
cnt[6] = 3
cnt[7] = 0
cnt[8] = 2

l2 = 1; r2 = 8
j = 1 => cnt[1] * (10 / 1 - (8 - 1) / 1) = 0
j = 2 => cnt[2] * (10 / 2 - (8 - 1) / 2) = 1 * 2 = 2 =>  (2;2;8), (2;2;10)
j = 3 => cnt[3] * (10 / 3 - (8 - 1) / 3) = 1 * 1 = 1 =>  (3;3;9)
j = 4 => cnt[4] * (10 / 4 - (8 - 1) / 4) = 2 * 1 = 2 => (2;4;8), (4;4;8)
j = 5 => cnt[5] * (10 / 5 - (8 - 1) / 5) = 1 * 1 = 1 => (5;5;10)
j = 6 => cnt[6] * (10 / 6 - (8 - 1) / 6) = 3 * 0 = 0
j = 7 => cnt[7] * (10 / 7 - (8 - 1) / 7) = 0 * 0 = 0
j = 8 => cnt[8] * (10 / 8 - (8 - 1) / 8) = 2 * 1 = 2 =>  (2;8;8), (4;8;8)
*/