#include <fstream>
using namespace std;

#define N 2000001

ifstream fin ("ciur.in");
ofstream fout("ciur.out");

bool a[N];
int prim[N];

int main()
{
    int n;
    fin >> n;
    for(int i = 4; i <= n; i += 2) a[i] = 1;
    for(int i = 3; i * i <= n; i += 2)
        if(a[i] == 0)
            for(int j = i * i; j <= n; j += 2 * i) a[j] = 1;
    int k = 0, l = 1;
    prim[++k] = 2;
    for(int i = 3; i <= n; i += 2)
        if(a[i] == 0) l++;
    fout << l;
    return 0;
}