#include <fstream>
using namespace std;

char ciur[2000005];
int n, nr;

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

int main()
{
    cin>>n;
    for ( int d = 2; d * d <= n; d++)
        if ( ciur[d] == 0 )
            for ( int i = d * d; i <= n; i = i + d )
                ciur[i] = 1;
    for(int i=2;i<=n;i++)
        if(ciur[i] == 0)
            nr++;
    cout<<nr;
    return 0;
}