#include <bits/stdc++.h>
using namespace std;
int sieve[2000005], cnt;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main(){    
    sieve[0] = 1; sieve[1] = 1; sieve[2] = 0;
    int n;
    in>>n;
    for (int i=4;i<=n;i+=2)
        sieve[i] = 1;
    for (int i=3;i<=n;i+=2){
        if (!sieve[i]){
            for (int x=2*i;x<=n;x+=i)
                sieve[x] = 1;
        }
    }
    for (int i=1;i<=n;++i)
        if (sieve[i] == 0) cnt++;
    out<<cnt;
}