#include <iostream>
#include <cstdio>

using namespace std;

int main()
{
    FILE *f = fopen("ciur.in", "r");
    freopen("ciur.out", "w", stdout);
    int n;
    fscanf(f, "%d", &n);
    bool *a = new bool[n+1];
    for(int i = 2; i <= n; i++)
        a[i] = true;
    int nr = 0;
    for(int i = 2; i <= n; i++)
        if(a[i] == true)
        {
            for(int j = i+i; j <= n; j+=i)
                a[j] = false;
            nr++;
        }
    cout << nr;
    return 0;
}