#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset < 2000005 > ciur;
int main()
{
    ios_base::sync_with_stdio(0);
    fin.tie(0);

    int n, cnt = 0;
    cin >> n;

    for (int i = 4; i <= n; i+=2)
        ciur [i] = 1;
    for (int i = 3; i*i <= n; i+=2)
        if (ciur[i]==0)
            for (int j = i*i; j <= 2*n; j+=i)
                ciur[j]=1;
    ciur[1] = 1;

    for (int i = 2; i <= n; i ++)
        if (ciur[i]==0)
            cnt++;

    cout << cnt;

    return 0;
}