#include <fstream>
using namespace std;
#define N 2000001
ifstream cin("ciur.in");
ofstream cout("ciur.out");
bool a[N];
int prim[N];
int main()
{
    int n;
    cin>>n;
    for(int i=4;i<=n;i+=2) a[i] = 1;
    for (int i=3;i*i<=n;i+=2)
        if(a[i]==0)
        for (int j=i*i;j<=n;j=j+2*i) a[j]=1;

    int k=0,l=1;
    prim[++k]=2;
    for (int i=3;i<=n;i+=2)
        if(a[i]==0) l++;

    cout<<l;
    return 0;
}