#include<iostream>
#include<bitset>
using namespace std;
//ifstream cin("ciur.in");
//ofstream cout("ciur.out");
#define M 2000005
bitset <M> bitsett;

int main(){
    int n, cnt=0;
    cin>>n;
    for(int i=2; i<=n; ++i)
        if(!bitsett[i]){
            ++cnt;
            for(int j=i+i; j<=n; j+=i)
                bitsett[j]=1;
        }
    cout<<cnt;
    return 0;
}