#include <fstream.h>
int main()
{
ifstream f("ciur.in");
ofstream g("ciur.out");
long long int n;
int i,nr=0,j;
char prim[2000005];
f>>n;
f.close();
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;
g.close();
return 0;
}