#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

unsigned int v[2000001];
int main() {

    int cont=0,i,j,n;
    fin>>n;
    for(i=2;i<=n;i++)
        v[i]=1;
    for(i=2;i<=n;i++){
        if(v[i]==1)
            ++cont;
        for(j=2*i;j<=n;j+=i)
            v[j]=0;
    }
    fout<<cont;

    return 0;
}