#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,i,j,nrt;
bool a[2000010];
void ciur()
{
    for (i=2;i<=n;i++)
     if (a[i]==0)   for (j=i+i;j<=n;j+=i) a[j]=1;
}

int main()
{
f>>n;
ciur();
for (i=2;i<=n;i++)
{
    nrt++;
}
g<<nrt;

    return 0;
}