#include <bits/stdc++.h>

using namespace std;

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n;
    scanf("%d",&n);
    vector<bool>ciur(n+1,0);
    auto eratostene=[&](){
        for(int i=2;i<=n;i++){
            if(!ciur[i]){// if is prime
                for(int j=i+i;j<=n;j+=i)
                    ciur[j]=1;
            }
        }
    };
    eratostene();
    int nr_prime=0;
    for(int i=2;i<=n;i++)
        if(!ciur[i])
            nr_prime++;
    printf("%d",nr_prime);

    return 0;
}