#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream gout("ciur.out");

int solve(int N)
{
    bool *P;
    P = new bool[N];
    for(int i=0;i<N;i++)
        P[i]=false;
    for(int i = 2;i<N;++i)
    {
        if(P[i]==false)
        for(int j = i+i; j<N; j+=i)
            P[j]=true;
    }
    int count = 0;
    for(int i=2;i<N;++i)
        if(P[i]==false)
            count++;
    return count;
}
int main()
{
    int n;
    fin>>n;
    gout<<solve(n);

    return 0;
}