#include <iostream>
#include <fstream>
using namespace std;
int main()
{
    ifstream A("ciur.in");
    ofstream B("ciur.out");
    int N,n=0;
    A>>N;
    int P[N];
    for (int i=2;i<=N;++i)
        P[i]=1;
    for (int i=2;i<=N;++i)
        if(P[i])
        {
            ++n;
            for(int j=2*i;j<=N;j+=i)
                P[j]=0;
        }
    B<<n;
    return 0;
}