#include <iostream>
#include <cstdio>
using namespace std;

bool sir[2000500];
int n;

void rez()
{
    int nr = 1;
    scanf("%d", &n);
    for(int i = 4; i<n; i+=2)
        sir[i] = 1;
    for(int i = 3; i<n; i+=2)
    {
        if(sir[i] == 0)
        {
            nr++;
            for(int j = i+i+i; j<n; j+=i)
                sir[j] = 1;
        }
    }
    printf("%d", nr);
}

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    rez();
    return 0;
}