#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <math.h>
#define dimmax 2000000000
#include <string.h>

using namespace std;

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


int main()
{   int n,i,j,nr=0;
    vector<bool> v;
    f >> n;
    v.assign(n+1,1);
    for(i=2;i*i<=n;i+=1)
        if(v[i])
            for(j=i*i;j<=n;j+=i)
                v[j]=0;
    for(i=2;i<=n;i++)
        if(v[i])
            nr++;
    g << nr << '\n';
    return 0;
}