#include <bits/stdc++.h>
using namespace std;
bitset <2000002> w; // SAU bool w[2000002];
int i, j, n, cnt;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f >> n;
    for(i = 2; i * i <= n; i ++)
        if(w[i] == false)
        {
            cnt ++;
            for(j = i * i; j <= n; j = j + i)
                w[j] = true;
        }
    g << cnt;
    f.close();
    g.close();
    return 0;
}