#include <iostream>
#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

#define N 2000001
int v[N];

int main()
{
    int n,i,j,cont=0;
    f>>n;
    for(i=2;i<=n;i++)
        if(v[i]==0)
            for(j=i*i;j<=n;j=j+i)
                v[j]=1;
    for(i=2;i<=n;i++)
        if(v[i]==0)
            cont++;
    g<<cont;

    return 0;
}