#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int x,i,j,k;
bool v[2000001];
int main()
{
    fin>>x;
    for(i=4;i<=x;i+=2)
        v[i]=1;
    for(i=2;i<=x;i++)
    {
        if(v[i]==0)
        for(j=2;j*i<=x;j++)
        {
            v[j*i]=1;
        }
    }
    for(i=2;i<=x;i++)
        if(v[i]==0) k++;
    fout<<k;


}