#include<fstream>
#include<algorithm>
#define N 2000100
#define FOR(a,b,c) for(register int a=b;a<=c;++a)
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int sol,n;
bool v[N];
int main ()
{
    f>>n;
    FOR(i,2,n)
    if(!v[i])
    {
        sol++;
        if(1LL*i*i>n)
            continue;
        for(int j=i*i;j<=n;j+=i)
            v[j]=1;
    }
    g<<sol;
    return 0;
}
//Look at me!Look at me!The monster inside me has grown this big!