Cod sursa(job #652438)
Utilizator | Alex Velea veleandu | Data | 24 decembrie 2011 14:48:44 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 100 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.5 kb |
#include<iostream>
#include<fstream>
#include<cmath>
using namespace std;
long n,i,j,s;
char V[250000];
ifstream in("ciur.in");
ofstream out("ciur.out");
int main()
{
in>>n;
for ( i=2; i<=sqrt(n); i++)
if ( (V[i>>3]&(1<<(i&7))) == 0 )
{
for ( j=i*i; j<=n; j+=i )
V[j>>3]|=(1<<(j&7));
}
for ( i=2; i<=n; ++i )
{
if ( (V[(i>>3)]&(1<<(i&7))) ==0 )
s++;
}
out<<s<<"\n";
return 0;
}