#include <iostream>
#include <fstream>

using namespace std;

#define MAX 2000010

bool prim[MAX] = {0};

int main()
{
    ifstream in("ciur.in");
    int n,p = 1,i;
    in >> n;
    for(int j = 3;j <= n; )
    {
        if(prim[j] == 0)
        {
            ++p;
            for(i=1;i*j<=n;++i)
            prim[i*j]=1;
        }
        while(prim[j] == 1 && j <= n)
            j+=2;
    }
    ofstream out("ciur.out");
    out << p;
    return 0;
}