#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n;
char prim[2000005];
int main(void)
{   int i, j;
	f>>n;
	int nr=0;
    for (i = 2; i <= n; ++i)
        prim[i] = 1;
    for (i = 2; i <= n; ++i)
        if (prim[i])
        {++nr;
		 for (j = i+i; j <= n; j += i) prim[j] = 0;
        }
    g<<nr<<"\n";
    return 0;
}