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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. int main() {
  5. long long n,k;
  6. cin>>n>>k;
  7. long long s=0;
  8. for (int i=k; i<=n; i+=k) {
  9. s+=i;
  10. }
  11. cout <<s;
  12. return 0;
  13. }
Success #stdin #stdout 0s 5328KB
stdin
15 5 
stdout
30