#include <iostream>
#include<fstream>
#define maxn 2000001
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

char prim[maxn];
int n;
int i,k=0;

void eratostene(int n)
{
    for(int p=2;p<n;p++)
    {
        if(prim[p]==0) {prim[p]=1; k++;}
        int c=2;
        int mul=p*c;
        while(mul<=n)
        {
            prim[mul]=-1;
            c++;
            mul=p*c;
        }
    }
}

int main()
{
    f>>n;
    eratostene(n);
    g<<k;

    return 0;
}