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  1. #include <bits/stdc++.h>
  2.  
  3. using namespace std;
  4.  
  5. #define file(NAME) if (fopen(NAME".inp", "r"))  freopen(NAME".inp", "r", stdin), freopen(NAME".out", "w", stdout)
  6. #define FOR(i, a, b) for (int i = (int) a; i <= (int) b; ++i)
  7. #define FOD(i, a, b) for (int i = (int) a; i >= (int) b; --i)
  8.  
  9. #define all(s) (s).begin(), (s).end()
  10. #define pb push_back
  11. #define ll long long
  12. #define fi first
  13. #define se second
  14. #define pii pair<int, int>
  15.  
  16. const int maxn = 1e5 + 5;
  17. const int N = 505;
  18. const int MOD = 1e9 + 7;
  19.  
  20.  
  21. ll n;
  22.  
  23.  
  24.  
  25.  
  26. ll power(ll a, ll b) {
  27.     ll res = 1;
  28.     while (b) {
  29.         if (b & 1) res = (res * a % MOD) % MOD;
  30.         a = (a * a) % MOD;
  31.         b >>= 1;
  32.     }
  33.  
  34.     return res;
  35. }
  36.  
  37.  
  38.  
  39.  
  40.  
  41.  
  42.  
  43.  
  44. // sum 1 -> n
  45. ll sum(ll n) {
  46.     // n * (n + 1) / 2
  47.     return (((n%MOD * (n+1)%MOD)%MOD) * power(2, MOD - 2)) % MOD;
  48. }
  49.  
  50.  
  51.  
  52.  
  53. ll calc(ll i, ll j, ll q) {
  54.     // (sum(j-1) - sum(i-1)) * q
  55.     return ((sum(j-1) - sum(i-1) + MOD)%MOD * q%MOD) % MOD;
  56. }
  57.  
  58.  
  59.  
  60.  
  61. signed main() {
  62.     cin.tie(0) -> sync_with_stdio(0);
  63.     file("x");
  64.  
  65.  
  66.     cin >> n;
  67.  
  68.  
  69.     ll ans = 0;
  70.  
  71.     ll i = 1;
  72.     while (i <= n) {
  73.         ll q = n / i;
  74.         ll j = n / q + 1;
  75.  
  76.         (ans += calc(i, j, q)) %= MOD;
  77.  
  78.         i = j;
  79.     }
  80.  
  81.     cout << ans;
  82.     return 0;
  83. }
Success #stdin #stdout 0.54s 5280KB
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736806794367
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640231665
https://ideone.com/ny8UIr
language:
C++14 (gcc 8.3)
created:
11 days ago
visibility:
public

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