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  1. #include<bits/stdc++.h>
  2. using namespace std ;
  3. long long demphanso( int n ){
  4.     if ( n <= 0 )
  5.         return 0 ;
  6.     vector<int> phi( n+1 ) ;
  7.     for ( int i = 0 ; i <= n ; i++ )
  8.         phi[i] = i ;
  9.     for ( int i = 2 ; i <= n ; i++ ){
  10.         if ( phi[i] == i ){
  11.             for ( int j = i ; j <= n ; j+=i ){
  12.                 phi[j] -= phi[j]/i ;
  13.             }
  14.         }
  15.     }
  16.     long long dem = 1 ;
  17.     for ( int i = 1 ; i <= n ;i++ )
  18.         dem += phi[i] ;
  19.     return dem ;
  20. }
  21. int main(){
  22.     int n ;
  23.     cin >> n ;
  24.     cout << demphanso(n) ;
  25. }
Success #stdin #stdout 0.01s 5320KB
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326307209
https://ideone.com/ekJEUf
language:
C++14 (gcc 8.3)
created:
6 days ago
visibility:
public

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