Cod sursa(job #1105681)
Utilizator | Data | 11 februarie 2014 23:25:50 | |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 10 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.42 kb |
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool a[2000001];
int main()
{
int n,i,k,nr=0;
for(i=4;i<=2000000;i+=2)
a[i]=1;
for(i=3;i<=1415;i+=2)
if(!a[i])
{
for(k=i*i;k<=2000000;k++)
a[k]=1;
}
fin>>n;
for(i=2;i<=n;i++)
if(!a[i]) nr++;
fout<<nr<<'\n';
return 0;
}