#include <iostream>
#include <fstream>
using namespace std;

int Prim[1000000];
int main() {
    int i,j,N,s=0;
    ifstream in("ciur.in");
    in>>N;
    ofstream out("ciur.out");
    for(i=2;i<=N;i++)
    if(!Prim[i])
    {
        s++;
        for(j=i;j<=N;j=j+i)
            Prim[j]=1;
    }
    
    out<<s;
    return 0;
}