#include <iostream>
#include <fstream>

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