Cod sursa(job #1581588)
Utilizator | Luca Stefan Ioan stefanst77 | Data | 26 ianuarie 2016 22:03:36 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 100 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.5 kb |
#include <fstream>
#include <bitset>
using namespace std;
bitset<2000002>a;
int main()
{
int n, i, k, j;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
fin >> n;
for (i=4; i<=n; i=i+2)
a[i]=1;
for (i=3; i*i<=n; i=i+2)
if (a[i]==0)
for (j=i*i; j<=n; j=j+2*i)
a[j]=1;
k=1;
for (i=3; i<=n; i=i+2)
if (a[i]==0)
k++;
fout << k << "\n";
fin.close();
fout.close();
return 0;
}