#include <bits/stdc++.h>
#define NMAX 2000001
using namespace std;

ifstream f ("ciur.in");
ofstream g ("ciur.out");

int n;
bool v[NMAX];

int main()
{
    f >> n;
    v[1] = 1;
    v[0] = 1;
    for(int i=2;i*i<=n;++i)
        if(v[i] == 0)
            for(int j=i+i;j<=n;j+=i)
                v[j] = 1;
    int nr = 0;
    for(int i=1;i<=n;++i)
        if(v[i] == 0)nr++;
    g << nr;

}