#include <iostream>

using namespace std;
//ifstream cin("ciur.in");
//ofstream cout("ciur.out");
bool eratostene[2000001];
int main()
{
    int n,nr=0;
    cin>>n;
    for(int d=2;d*d<=n;d++)
    {
        if(eratostene[d]==1)
        {
            continue;
        }
        for(int i=d*2;i<=n;i+=d)
        {
            eratostene[i]=1;
        }
    }
    for(int i=2;i<=n;i++)
    {
        if(eratostene[i]==0)
            nr++;
    }
    cout<<nr;
}