#include <fstream>
using namespace std;
int ver[2000000]={0},nr;
int main()
{
    ifstream f("ciur.in");
    ofstream c("ciur.out");
    long long n,i,j;
    f>>n;
    nr=1;
    for(i=4;i<=n;i+=2)
        ver[i]=1;
    for(i=3;i<=n;i+=2)
        if(ver[i]!=1)
            for(j=i*i;j<=n;j+=2*i)
                ver[j]=1;
    for(i=3;i<=n;i+=2)
        if(ver[i]!=1)
            nr++;
    c<<nr;
    f.close();
    c.close();
    return 0;
}