#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int x, cate, j, n, i, d, cate1;
bool b[2000003];
int main()
{
    f>>n;
    b[1]=1;
    cate=0;
    for(i=2;i*i<=n;i++)
    {
        j=i;
        if(b[i]==0)
            while(i*j<=n)
            {
                b[i*j]=1;
                j++;
            }
    }
    for(i=1;i<=n;i++)
        if(b[i]==0)
            cate++;
    g<<cate;
    return 0;
}