#include <fstream.h>
ifstream fin("ciur.in");
ofstream fout("ciur.out");
char a[2000001];
long i=1,n,j,nr;
int main() {
    fin>>n;
    for(i=1;i<=n;++i)
        a[i]=1; //atribuim fiecarui element din vector valoarea 1
    for(i=2;i<=n;++i)
        if(a[i]==1) {
            nr++;
            for(j=2*i;j<=n;j+=i)
                a[j]=0;
        }
    fout<<nr;
    fin.close();
    fout.close();
    return 0;  
}