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  1. #include <bits/stdc++.h>
  2. #define VuDucNam ios_base::sync_with_stdio(false);
  3. #define Lop9a6 cin.tie(NULL);
  4. #define THCSPhamVanDong cout.tie(NULL);
  5. #define ll long long
  6. #define el cout << '\n'
  7. #define sz(a) (ll) a.size()
  8. #define all(a) a.begin(), a.end()
  9. #define fill(a, x) memset(a, x, sizeof(a))
  10. #define file(name) if (freopen(name ".inp", "r", stdin) freopen(name ".out", "w", stdout);
  11. #define TIME (1.0 * clock() / CLOCKS_PER_SEC)
  12.  
  13. using namespace std;
  14.  
  15. int main()
  16. {
  17.     VuDucNam Lop9a6 THCSPhamVanDong
  18.     ll n;
  19.     cin >> n;
  20.     ll ans = 0;
  21.     for (ll y = 1; y * y <= n; ++y)
  22.     {
  23.         ll x=n/y;
  24.         ans+=x*(x-1)/2;
  25.     }
  26.     cout << ans;
  27.     el;
  28.     return 0;
  29. }
  30.  
Success #stdin #stdout 0.01s 5288KB
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https://ideone.com/gTubUe
language:
C++ (gcc 8.3)
created:
38 days ago
visibility:
public

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