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  1. #include <bits/stdc++.h>
  2. #define ull unsigned long long
  3. #define ll long long
  4. #define el endl
  5. #define nl '\n'
  6. #define all(v) v.begin(), v.end()
  7. using namespace std;
  8.  
  9. void input()
  10. {
  11.     if (fopen("in.txt", "r"))
  12.     {
  13.         freopen("in.txt", "r", stdin);
  14.         freopen("out.txt", "w", stdout);
  15.     }
  16. }
  17.  
  18. void init()
  19. {
  20.     ios_base::sync_with_stdio(false);
  21.     cin.tie(nullptr);
  22. }
  23. int main()
  24. {
  25. Fast:
  26.     input();
  27.     init();
  28.     //---------------------------------------------------------------------------------------------------------------
  29.     int r = 0;
  30.     cin >> r;
  31.     const double Pi = 3.14159;
  32.     cout << Pi * pow(r, 2) << nl;
  33.  
  34.     return 0;
  35. }
Success #stdin #stdout 0s 5320KB
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https://ideone.com/FRpQpf
language:
C++ (gcc 8.3)
created:
1 hour ago
visibility:
public

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