# Cod sursa(job #153536)

Utilizator Data 10 martie 2008 16:38:04 Ciurul lui Eratosthenes 100 cpp done Arhiva educationala 1.07 kb
#include <cstdio>
#include <vector>

using namespace std;

typedef long long LL;
typedef vector<int> vi;
typedef vector< vi > vii;
typedef vector<string> vs;
typedef vector<double> vd;
typedef pair<int, int> ii;
#define PB push_back
#define SZ(v) v.size()
#define ALL(v) (v).begin(), (v).end()
#define FORIT(i,c) for (typeof((c).end()) i=(c).begin(); i!=(c).end(); ++i)
#define FOR(i,n) for (int i = 0; i<(n); ++i)
#define FORE(i,n) for (int i = 0; i<=(n); ++i)
#define FORI(i,n1,n2) for (int i = n1; i<(n2); ++i)
#define FORIE(i,n1,n2) for (int i = n1; i<=(n2); ++i)
#define FORV(i,v) for (unsigned int i = 0; i<SZ(v); ++i)

#define INF 0x3f3f3f3f
#define EPS 1e-9

#define NMAX 2000000

int N;
bool A[NMAX];

int main()
{
freopen("ciur.in", "r", stdin);
freopen("ciur.out", "w", stdout);

scanf("%d", &N);

int sol = 0;

FORIE(i, 2, N)
{
if (!A[i])
{
++sol;
for (int j = 2*i; j<=N; j+=i)
A[j] = 1;

}

}

printf("%d\n", sol);

return 0;
}