#include<fstream>
using namespace std;
   
    ifstream f("ciur.in");
    ofstream g("ciur.out");
		char prim[2000003];
		int numar, N;
		int main()
		{
    int i, j;
		f>>N;
    for(i = 3 ; i <= N ; i = i + 2)
        if(prim[i] == 0)
					{numar++;
             for(j= 2 * i ; j <= N ; j = j + i)
     		       prim[j] = 1;
          }
		numar++;
    g<<numar;
    return 0;
		}