#include <iostream>
#include <cstdio>
#include <vector>
using namespace std;
int main()
{
    int i,ct=0,n,j;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    vector <bool> v(n,false);
    for(i=2;i<n;i++)
        if(v[i]==false)
            for(j=i+i;j<n;j=j+i)
                v[j]=true;
        for (i=2;i<n;i++)
            if (v[i]==false) ct++;
    printf("%d",ct);
    return 0;
}