#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,cnt;
bool prim[2000005];

int main()
{
    int i,j;
    fin>>n;
    cnt=1;
    for (j=2;j<=n;j+=2)
        prim[j]=1;
    for (i=3;i<=n;i+=2)
        if (!prim[i])
            {
                cnt++;
                for (j=i;j<=n;j+=i)
                    prim[j]=1;
            }
    fout<<cnt<<"\n";
    return 0;
}