//http://www.infoarena.ro/problema/ciur
#include <fstream>
#include <bitset>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bitset <2000001> v;
int main()
{
    int nr = 1,i,n,j;
  
    in >> n;
    for( i = 3; i*i <= n; i += 2)  
        if( v[i] == 0 )            
            for(j = i*i; j <= n ;j += 2*i) 
                v[j] = 1;          
    for(i = 3; i <= n ;i += 2)      
        if(v[i] == 0)
            nr++;
    out << nr;
    return 0;
}