Cod sursa(job #899337)
Utilizator | stardust stardust | Data | 28 februarie 2013 14:00:54 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 100 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.43 kb |
#include <fstream>
#include <bitset>
#include <cmath>
#define maxn 2000010
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bitset<maxn>ciur;
int n;
void solve()
{
for(int i=3;i<=sqrt(maxn);i+=2)
for(int j=i*i;j<=maxn;j+=i)
ciur[j]=1;
}
int main()
{
in>>n;
solve();
int nr=1;
for(int i=3;i<=n;i+=2)
if(ciur[i]==0) nr++;
out<<nr;
return 0;
}