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  1. // ~~ icebear ~~
  2. #include <bits/stdc++.h>
  3. using namespace std;
  4. #define int long long
  5.  
  6. typedef long long ll;
  7. typedef pair<int, int> ii;
  8. typedef pair<ii, int> iii;
  9.  
  10. #define FOR(i,a,b) for(int i=a; i<=b; ++i)
  11. #define FORR(i,a,b) for(int i=a; i>=b; --i)
  12. #define rep(i, n) for(int i=0; i<n; ++i)
  13. #define red(i, n) for(int i=n-1; i>=0; --i)
  14. #define mp make_pair
  15. #define pb push_back
  16. #define fi first
  17. #define se second
  18. #define task "icebearat"
  19.  
  20. const int MOD = 1e9 + 7;
  21. const int inf = 1e9 + 27092008;
  22. const ll LLinf = 1e18 + 27092008;
  23.  
  24. int pw(int x, int k){
  25. 	int res = 1;
  26. 	while(k){
  27. 		if (k & 1) res = res * x % MOD;
  28. 		x = x * x % MOD;
  29. 		k >>= 1;
  30. 	}
  31. 	return res;
  32. }
  33.  
  34. int sum(int l, int r){ // tính tổng từ l -> r
  35. 	l %= MOD;
  36. 	r %= MOD;
  37. 	// pw(2, MOD - 2) : nghịch đảo modulo.  1/a = a^(-1) đồng dư với a^(MOD - 2) theo modulo MOD
  38. 	return (r  * (r + 1) % MOD * pw(2, MOD - 2) % MOD - l * (l - 1 + MOD) % MOD * pw(2, MOD - 2) % MOD + MOD) % MOD;
  39. }
  40.  
  41. int solve1(int n){
  42. 	int l = 1, res = 0;
  43. 	while(l <= n){
  44. 		int k = n / l;
  45. 		int r = n / k;
  46. 		res = (res + k * sum(l, r) % MOD) % MOD;
  47. 		l = r + 1;
  48. 	}
  49. 	return res;
  50. }
  51.  
  52. void solve(){
  53. 	int n; cin >> n;
  54. 	cout << solve1(n);
  55. }
  56.  
  57. signed main(){
  58.     ios_base::sync_with_stdio(0);
  59.     cin.tie(0); cout.tie(0);
  60.     if (fopen(task".inp", "r")){
  61.         freopen(task".inp", "r", stdin);
  62.         freopen(task".out", "w", stdout);
  63.     }
  64.     int tc = 1;
  65. //     cin >> tc;
  66.     while(tc--) solve();
  67.     return 0;
  68. }
  69.  
Success #stdin #stdout 4.92s 5320KB
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https://ideone.com/bcfs6U
language:
C++14 (gcc 8.3)
created:
3 days ago
visibility:
public

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