#include    <fstream>
#include    <bitset>
using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

bitset < 100000005 > ciur;

int main()
{
    for (int i = 4; i <= 10000000; i+=2)
        ciur [i] = 1;
    for (int i = 3; i*i <= 10000000; i+=2)
        if (ciur[i]==0)
            for (int j = i*i; j <= 2000000; j+=i )
                ciur[j]=1;
    int n,cnt=0;
    cin >> n;
    for (int i = 2; i <= n; i ++)
        if (ciur[i]==0)
            cnt++;
        cout << cnt;
    return 0;
}