#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 <int> v(n,1);
    for(i = 2; i< n; i++)
        if(v[i] == 1)
            for( j = i+i; j < n; j += i)
                v[j]=0;
        for (i=2;i<n;i++)
            if (v[i]==1) ct++;
    printf("%d",ct);
    return 0;
}