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#include<bits/stdc++.h>
#define in f
#define out g
using namespace std;
ifstream f ("ciur.in");
ofstream g ("ciur.out");
int const maxsize = 2000010;
int n, k;
unordered_map<int, bool> used;
int main() {
in >> n;
for (int i = 2; i <= n; i++) {
if (used[i] == false)
k++;
for (int j = i; j <= n; j += i) {
used[j] = true;
}
}
out << k;
}