Cod sursa(job #3175772)
Utilizator | Andrei Mircea Andrei1209 | Data | 26 noiembrie 2023 13:28:21 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 0 |
Compilator | cpp-64 | Status | done |
Runda | Arhiva educationala | Marime | 0.53 kb |
#include <fstream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
const int nmax = 1000000;
bool ciur[nmax + 5];
int main()
{
int i, n, j;
ciur[0] = 1;
for ( i = 3; i * i <= nmax; i += 2 )
if ( ciur[i / 2] == 0 )
for ( j = i * i; j <= nmax; j += 2 * i )
ciur[j / 2] = 1;
cin >> n;
int cnt =0;
for ( i = 2; i <= n; ++i )
if ( ciur[i / 2] == 0 && i % 2 == 1 )
++cnt;
cout << cnt << endl;
return 0;
}