#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000001];
int main()
{
    int n,i,j,gigel=0;
    in>>n;

for(i=2;i<=n; i++)
{
v[i] =2;
}
for (i=2;i<=n;i++)
{
    if(v[i] == 1)

         for(j=2;j*i <= n;j ++)
         {
         v[i*j] = 0;
         }
}
for(i=1;i<=n; i++)
{
    if(v[i] ==1)
    gigel++;

}
out<<gigel;
    return 0;
}