#include <fstream>

using namespace std;

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

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

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

return 0;
}