#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,nr,i,j,v[2000001];
int main()
{
    fin>>n;
    for(i=3; i*i<=n; i+=2)
        if(v[i]==0)
            for(j=3; j<=n/i; j+=2)
                v[i*j]=1;
    nr=1;
    for(i=3; i<=n; i+=2)
        if(v[i]==0)
            nr++;
    fout<<nr;
    return 0;
}