#include <iostream>
#include <fstream>
#include <bitset>
using namespace std;
ifstream f("ciur.in"); ofstream g("ciur.out");
bitset <2000001> v;
int main()
{
    int n, i, c=0, j;
    f>>n;
    v[0]=v[1]=1;
    for (i=2;i<=2000000;i++)
    {
        if (v[i]==0)
        {
            for (j=i*2;j<=2000000;j+=i)
            {
                v[j]=1;
            }
        }
    }
    for (i=1;i<=n;i++)
    {
        if (v[i]!=1) c++;
    }
    g<<c;
    return 0;
}