#include <fstream>
#include <iostream>
#include<cmath>
using namespace std;
int main() {
ifstream in("ciur.in");
ofstream out("ciur.out");
bool c[2000001];
int p=0,n,i,j;
in>>n;
for (i=2;i<=sqrt(n);i++){
        if(!c[i]){
                for(j=i*i;j<=n;j+=i)
                    c[j]=true;
        }
}
for(i=2;i<=n;i++)
    if(!c[i]) p++;
out<<p;
in.close();
out.close();
return 0;
}