#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,i,j,c;
char x[2000000];
int main()
{
f>>n;
for(i=1;i<=n;i++)
       x[i]=1;

for   (i=2;i<=n;i++)
          if(x[i]==1) {c++;
                      for(j=i+i;j<=n;j=j+i)
                      x[j]=0;
                      }
          g<<c;

    return 0;
}