#include <fstream>
#include <math.h>

using namespace std;
int main()
{

ifstream f("ciur.in");
ofstream g("ciur.out");
       
long int i,j,n;
f>>n;
char A[n+1];

for (i=1;i<=n;i++) A[i] = 1;

for (i=2;i<=n;i++)
if (A[i]) for (j=2;j*i<=n;j++) A[j*i] = 0;

long int S=0;
for (i=2;i<=n;i++) if (A[i]) S++;

g<<S;

f.close();
g.close();    
}