#include<iostream>
#include<fstream>
using namespace std;
ifstream f("ciur.in");
ofstream out("ciur.out");

char v[2000001]={1,1};
int main(){
    int x,i,j,k=0;
    f>>x;
    for(i=2;i*i<=x;i++)
        if(!v[i])
            for(j=i*i;j<=x;j+=i)
                v[j]=1;
    for(i=2;i<=x;i++)
        if(!v[i])
            k++;
    out<<k;
    return 0;
}