#include <fstream>
#include <iostream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,p;
bool v[2000001];
int main()
{
    //cout << sizeof(v)*1.0/1024;
    fin >> n;
    v[0]=v[1]=0;
    for(int i=2;i*i<=2000000;i++)
    {
        if(v[i]==0)
        {
            for(int j=2;j*i<=2000000;j++)
            {
                v[i*j]=1;
            }
        }
    }
    for(int i=2;i<=n;i++)
    {
        if(v[i]==0) p++;
    }
    fout << p;
    return 0;
}