#include<bits/stdc++.h>
using namespace std;
long long n;
bool isprime[100000001];
vector<long long> primes;
void shai(){
    for(long long i=2;i<=n;i++){
        if(isprime[i]) primes.push_back(i);
        for(long long j=0;j<primes.size()&&i*primes[j]<=n;j++){
            isprime[i*primes[j]]=false;
            if(i%primes[j]==0) break;
        }
    }
}
int main(){
    cin>>n;
    memset(isprime,true,sizeof(isprime));
    shai();
    cout<<primes.size();
    return 0;
}