#include <fstream>

using namespace std;

int a[2000003];

int main()
{
    int n,i,j,cnt;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    for(i=2;i*i<=n;++i)
        if(a[i]==0)
            for(j=i*i;j<=n;j=j+i)
                a[j] = 1;
    cnt = 0;
    for(i=2;i<=n;++i)
        if(a[i]==0) cnt++;
    fout<<cnt<<"\n";
    fin.close();
    fout.close();
    return 0;
}