#include <iostream>
#include <cstdio>
using namespace std;
int v[2000001];
int main()
{
    long int a,i,j;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int cnt=1;

    cin >> a;
    for(i=3;i<=a;i+=2)
    {
        if(v[i]==0) cnt++;
        for(j=i+i+i;j<=a;j+=i<<1)
            v[j]=1;

    }
    cout << cnt;
    return 0;
}