#include <fstream>
#include <cmath>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");

bool x[2000001];
int n, i, j, k, r;

int main()
{
    cin>>n;
    k=1;
    r=sqrt(n);
    for(i=4; i<=n; i+=2) x[i]=1;
    for(i=3; i<=n; i+=2)
        if(x[i]==0)
        {
            k++;
            if(i<=r)
                for(j=i*i; j<=n; j+=i) x[j]=1;
        }
    cout<<k;
    return 0;
}