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  1. #include <iostream>
  2. #include <vector>
  3. #include <cmath>
  4. #include <stdio.h>
  5.  
  6. using namespace std;
  7.  
  8. void fast_io(){
  9.     ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
  10. }
  11.  
  12. int main()
  13. {
  14.     fast_io();
  15.     long long Sn;
  16.     #ifdef ONLINE_JUDGE
  17.         cin >> Sn;
  18.     #endif
  19.     #ifndef ONLINE_JUDGE
  20.         Sn = 15;
  21.     #endif
  22.     // n^2 + n - 2Sn = 0
  23.     double n1 = (-1+sqrt(1-(4*1*-2*Sn)))/2;
  24.     double n2 = (-1-sqrt(1-(4*1*-2*Sn)))/2;
  25.     cout << floor(max(n1, n2));
  26. }
  27.  
Success #stdin #stdout 0.01s 5284KB
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stdin
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15
stdout
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5
https://ideone.com/A8jHcV
language:
C++ (gcc 8.3)
created:
9 days ago
visibility:
public

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