#include <bits/stdc++.h>

using namespace std;
int n,ciur[2000001],cnt;
int main() {
    ofstream cout("ciur.out");
    ifstream cin("ciur.in");
    ciur[0] = ciur[1] = 1;
    for(int i = 2;i<=2000001;i++)
    {
        if(ciur[i] == 0)
        {
            for(int j = 2*i;j<=2000001;j+=i)
            {
                ciur[j] = 1;
            }
        }
    }
    cin >> n;
    cnt = 0;
    for(int i =2;i<=n;i++)
    {
        if(ciur[i] == 0)
        {
            cnt++;
        }
    }
    cout << cnt;
}