#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bool v[2000005];
int main()
{
    int n,cont=0,i,j;
    f>>n;
    for (i=2;i<=sqrt(n);i++)
    {
        if (v[i]==0)
            for(j=i*2;j<=n;j=j+i)
                v[j]=1;
    }
    for (i=2;i<=n;i++){
        if(v[i]==0) cont++;
    }
    g<<cont;
    return 0;
}