Cod sursa(job #1307703)

Utilizator diana-t95FMI Tudoreanu Diana Elena diana-t95 Data 2 ianuarie 2015 18:11:18
Problema Ciurul lui Eratosthenes Scor 0
Compilator cpp Status done
Runda Arhiva educationala Marime 0.35 kb
Raporteaza aceasta sursa 
#include <iostream>
#include <fstream>
#include <bitset>
using namespace std;
#define maxn 2000000
int N;
bitset<maxn> b;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    cin>>N;
    int i, j, ans=1;
    for (i=3;i*i<=N;i+=2)
        if (!b[i]) for (j=i*i;j<=N;j+=2*i) b[j]=1;
    cout<<(N+1)/2-b.count()<<'\n';
}