Cod sursa(job #790623)
Utilizator | Campeanu Vlad vld7 | Data | 21 septembrie 2012 22:35:55 |
---|---|---|---|
Problema | Ciurul lui Eratosthenes | Scor | 100 |
Compilator | cpp | Status | done |
Runda | Arhiva educationala | Marime | 0.51 kb |
#include <cstdio>
#define maxN 2000005
using namespace std;
FILE *f = fopen ("ciur.in","r");
FILE *g = fopen ("ciur.out","w");
int n, sol;
bool prim[maxN];
int main()
{
fscanf (f, "%d", &n);
for (int i = 2; i <= n; i++)
prim[i] = true;
for (int i = 2; i * i <= n; i++)
if (prim[i]) {
for (int j = i * i; j <= n; j += i)
prim[j] = 0;
}
for (int i = 2; i <= n; i++)
if (prim[i])
sol++;
fprintf (g, "%d\n", sol);
fclose(f);
fclose(g);
return 0;
}