#include<iostream>
#include<fstream>
using namespace std;
bool v[1000001];
int n,i,j,c=0;
ifstream in("ciur.in");
ofstream out("ciur.out");


int main()
{in>>n;
for(i=2;i<=n;i++)
    if (v[i]==0){
    c++;
    for(j=i;j<=n;j+=i)
        v[j]=1;
    }

 out<<c;

return 0;

}