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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int main() {
  5. int n;
  6. cin>>n;
  7. n=n*2;
  8. int m=sqrt(n);
  9. int p=m*(m-1);
  10. int q=m*(m+1);
  11.  
  12. if(p==n||q==n)
  13. cout<<"YES\n";
  14. else
  15. cout<<"NO\n";
  16. 	// your code goes here
  17. 	return 0;
  18. }
Success #stdin #stdout 0s 4304KB
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Standard input is empty
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YES
https://ideone.com/BZXQLt
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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