#include<fstream>
#include<stdlib.h>
using namespace std;
int main(){
    ifstream in("ciur.txt");
    ofstream out("ciur.out");
    int i,g=0,j,n;

    in>>n;

    int *v = (int*)calloc (n, sizeof(int));
    for(i=2;i<=n;i++)
        if(v[i]==0)
        {
        for(j=2*i;j<=n;j=j+i)
            v[j]=1;
        g++;
        }
    out<<g;
    in.close();
    out.close();
    return 0;
}