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  1. //#pragma GCC optimize("Ofast")
  2. //#pragma GCC target("avx,avx2,fma")
  3. #include <bits/stdc++.h>
  4. using namespace std;
  5. #define ll long long
  6. #define fi first
  7. #define se second
  8. #define MOD 1000000007
  9. #define FOR(i,a,b) for (int i = (a);i <= (b);i++)
  10. #define FOD(i,a,b) for (int i = (b);i >= (a);i--)
  11. #define ALL(x) (x).begin(),(x).end()
  12. #define ii pair<ll,ll>
  13. #define iii pair<ll,pair<ll,int>>
  14. //const int MOD = 998244353;
  15. const int MAXN = 2e5 + 7;
  16. int a[MAXN];
  17. ll calc(ll x,ll y,ll k){
  18.     if (x > y)return 0;
  19.     ll n = (y - x) / k + 1;
  20.     return n * (x + y) / 2;
  21. }
  22. int main(){
  23.     ios_base::sync_with_stdio(false);
  24.     cin.tie(0); cout.tie(0);
  25.     //freopen("COMNUM.inp","r",stdin);
  26.     //freopen("COMNUM.out","w",stdout);
  27.     ll n,k;cin >> n >> k;
  28.     ll l = (n + k + 1) / k * k,r = 2 * n / k * k;
  29.     ll u = n - (r - n) + 1,v = n - (l - n) + 1;
  30.     cout << calc(k - 1,(n + 1) / k * k - 1,k) + calc(u,v,k);
  31.     return 0^0;
  32. }
Success #stdin #stdout 0.01s 5288KB
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46990987004369
https://ideone.com/81BhBv
language:
C++ (gcc 8.3)
created:
4 hours ago
visibility:
public

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