#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool v[2000005];
int i,j,n,s;
void ciur ()
{
v[1] = 1;
for (i = 2;i*i <= n; i ++)
{
if (v[i]==0)

    for(j=i*i;j<=n;j+=i){
        v[j]=1;
        }
}}
int main()
{
int cnt = 0;
    in>>n;
    ciur();
    for (i = 1; i <= n; i ++)
    {
    if(v[i]==0)
    cnt ++;
    }
    out<<cnt;
    return 0;
}