Cod sursa(job #665019)

Utilizator nutipasa16Macovei Claudiu nutipasa16 Data 21 ianuarie 2012 13:51:09
Problema Ciurul lui Eratosthenes Scor 100
Compilator cpp Status done
Runda Arhiva educationala Marime 0.35 kb
Raporteaza aceasta sursa 
#include<fstream>
#include<bitset>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n,x;
bitset<2000001> v;
int main()
	{in>>n;
	v.reset();
	for(int i=4;i<=n;i+=2)v.flip(i);
	for(int i=3;i<=n;i+=2)if(v[i]==0)for(int j=3*i;j<=n;j+=i)if(v[j]==0)v.flip(j);
	out<<n-v.count()-1<<'\n';
	out.close();
	return 0;
	}