#include <iostream>
#include <cstdio>

using namespace std;

bool a[2000010];

int main()
{
    int n;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    cin>>n;
    for(int i=2;i*i<=n;i++)
        if(!a[i])
            for(int j=i*i;j<=n;j+=i)
                a[j]=1;
    int nr=0;
    for(int i=2;i<=n;i++)
        if(!a[i])
            nr++;
    cout<<nr<<"\n";
    return 0;
}