#include<bits/stdc++.h>
using namespace std;
int n, k;
bool ciur[2000000];
int main(){
    int i, prim=2;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    cin>>n;
    ciur[0]=1;
    ciur[1]=1;

    while(prim*prim<=n){
        if(ciur[prim]==0){
            k++;
            for(i=prim*prim;i<=n;i+=prim)
                ciur[i]=1;}
        prim++;
    }



    cout<<k;
    return 0;

}