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

const int N = 2000000;
bool ciur[N + 1];
int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n,i,j,nr=0;
    fin >> n;
    for(int i = 2; i <= n; i++)
    {
        if(ciur[i] == 0)
        {
            for(j = i * 2; j <= n; j+=i)
                ciur[j] = 1;
            nr++;
        }
    }
    fout << nr;
    return 0;
}