#include <iostream>
#include <fstream>
using namespace std;

int n,cnt=0;
char prim[2000005];

int main()
{
    int i,j;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for (i=2;i<=n;i++)
        prim[i]=1;
    for (i=2;i<=n;i++)
        if (prim[i])
    {
        cnt++;
        for (j=i+i;j<=n;j+=i)
            prim[j]=0;
    }
    g<<cnt;
    f.close();
    g.close();
    return 0;
}