#include <bits/stdc++.h>

using namespace std;
char prim[2000001];
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n,nr=0;
    f>>n;
    for (int i=2;i<=n;++i)
    {
        prim[i]=i;
    }
    for (int i=2;i<=n;++i)
    {
        if (prim[i])
        {
            nr++;
            for (int j=i+i;j<=n;j+=i)
            {
                prim[j]=0;
            }
        }
    }
    g<<nr;
    return 0;
}