#include <bits/stdc++.h>
using namespace std;
int steve[1000005], cnt;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main(){    
    steve[0] = 1; steve[1] = 1;
    int n;
    in>>n;
    for (int i=2;i<=n;++i){
        if (!steve[i]){
            for (int x=2*i;x<=n;x+=i)
                steve[x] = 1;
            cnt++;
        }
    }
    out<<cnt;
}