52 lines
897 B
C++
52 lines
897 B
C++
#include <iostream>
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using namespace std;
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using ll = long long;
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ll N;
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ll ans;
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void init();
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void solve();
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int main() {
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ios_base::sync_with_stdio(0);
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cin.tie(0); cout.tie(0);
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init();
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solve();
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cout << ans << "\n";
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}
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void init() {
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cin >> N;
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}
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void solve() {
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ll temp = 0;
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if (N % 6 == 0) {
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temp += N*(N-1)*(N-2) / 6;
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temp -= N/3;
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temp -= ((N-4)/2) * N;
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temp /= N;
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temp += (N-2)/2;
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} else if (N % 3 == 0) {
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temp += N*(N-1)*(N-2) / 6;
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temp -= N/3;
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temp -= ((N-3)/2) * N;
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temp /= N;
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temp += (N-1)/2;
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} else if (N % 2 == 0){
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temp += N*(N-1)*(N-2) / 6;
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temp -= ((N-2)/2)*N;
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temp /= N;
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temp += (N-2)/2;
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} else {
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temp += N*(N-1)*(N-2) / 6;
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temp -= ((N-1)/2) * N;
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temp /= N;
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temp += (N-1)/2;
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}
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ans = temp;
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} |