#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#define test " test "
#define ll long long
#define pii pair<int, int>
#define FASTIO   \
    cin.tie(0);  \
    cout.tie(0); \
    ios_base::sync_with_stdio(0);
#define FILES                      \
    freopen("ciur.in", "r", stdin); \
    freopen("ciur.out", "w", stdout);
#define testcase             \
    int T;    \
    cin >> T; \
    while (T--)
#define vec vector<int>
using namespace std;

bool ciur[2000005];
int ind = 0;

int prec(int n)
{
    int cnt = 0;
    ciur[1] = ciur[0] = 1;
    for(int i = 2; i * i <= n; i++)
        if(!ciur[i])
        {
            cnt++;
            for(int j = i * i; j <= n; j += i)
                ciur[j] = 1;
        }
    return cnt;
}


signed main()
{
    FILES
    int n;
    cin >> n;
    cout << prec(n);
}