Cod sursa(job #777657)
Utilizator | Stf Cic icb_mn | Data | 12 august 2012 22:49:43 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 60 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.51 kb |
#include<fstream>
#include<malloc.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
#define NMAX 20000000
int n = 0,nr = 0;
short a[NMAX];
void eratosthenes()
{
for(int i = 4; i <= n; i+=2)
a[i] = 1;
for(int i = 3; i <= n; i += 2)
{
if(!a[i])
{
for(int j = i + i + i; j <= n; j += i + i )
a[j] = 1;
}
}
}
int main()
{
f>>n;
eratosthenes();
for(int i = 2; i <= n; ++i)
if(a[i] == 0)
nr++;
g<<nr;
g.close();
return 0;
}