#include <fstream>

using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
char ciur[2000000];
int main()
{
    long long int N,d,i,c=0;
    in>>N;
    for (d=2;d*d<=N;d++)
        if (ciur[d]==0)
            for (i=d*d;i<=N;i=i+d)
                ciur [i]=1;
    for(d=2;d<=N;d++)
    if(ciur[d]==0)
    c++;
    out<<c;
    return 0;
}