#include <fstream>
#include <bitset>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
	int n,i,j,cnt;
    bitset <2000050> ciur;
    fin>>n;
    ciur[0]=1;
    ciur[1]=1;
    for (i=2;i*i<=n;++i)
        if (!ciur[i])
            for (j=i;j<=n/i;++j)
                 ciur[i*j]=1;
    for (i=2;i<=n;++i)
        if (!ciur[i]) cnt++;
    fout<<cnt<<endl;
}