#include <vector>
#include <cstdio>
using namespace std;
vector<bool> ciur;
int n;
int main() {
freopen("ciur.in", "r", stdin);
freopen("ciur.out", "w", stdout);
scanf("%d", &n);
ciur.resize(n + 5, 1);
for (int i = 2; i < n; ++i)
for (int j = i * 2; j <= n; j += i)
ciur[j] = 0; 
int count = 0;
for (int i = 2; i <= n; ++i)
count += ciur[i];
printf("%d\n", count);
}