#include <iostream>

using namespace std;
bool freq[2000005];
int Ciur(int n)
{
    int ans = 1;
    for(int i = 3; i <= n; i += 2) {
        if(!freq[i]) {
            ++ans;
            for(int j = 3; j * i <= n; j += 2) freq[i * j] = 1;
        }
    }
    return ans;
}
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n;
    scanf("%d", &n);
    printf("%d", Ciur(n));
    return 0;
}