#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bool v[2000001];
void ciur()
{
    int i,j,n,nr=1;
    f>>n;
    for(i=3;i<=n/2;i+=2)
        if(v[i]!=1)
            for(j=2;j<=n/i;++j)
                v[i*j]=1;
    for(i=3;i<=n;i+=2)
        if(v[i]==0)
            ++nr;
    g<<nr;
}
int main()
{
    ciur();
    return 0;
}