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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. using ll = long long;
  4. vector<bool>isPrime;
  5. void seive(int n){
  6. 	isPrime.resize(n+1,true);
  7. 	isPrime[0] = isPrime[1] = false;
  8. 	for(int i = 2 ; i < n ;i++ ){
  9. 		if(isPrime[i]){
  10. 			for(int j = i*i ; j < n ;j+=i){
  11. 				isPrime[j]=false;
  12. 			}
  13. 		}
  14. 	}
  15. }
  16. int main() {
  17. 	int n;
  18. 	cin>>n;
  19. 	seive(n);
  20. 	int p;
  21. 	for(int i = n-1 ; i>=0 ;i--){
  22. 		if(isPrime[i]){
  23. 			p = i;
  24. 			break;
  25. 		}
  26. 	}
  27. 	cout<<"p: "<<p <<endl;
  28. 	ll d = 1LL*p*n;
  29. 	cout<<"d : " <<d <<endl;
  30. 	ll ans = 0;
  31. 	if(d%2 == 0)ans = d/2;
  32. 	else ans =((n-1)*p+2)/2;
  33.  
  34. 	cout<<ans;
  35. }
Success #stdin #stdout 0s 5320KB
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stdin
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7
stdout
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p: 5
d : 35
16
https://ideone.com/V9dH3c
language:
C++ (gcc 8.3)
created:
2 days ago
visibility:
public

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