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#include <iostream>
#include <fstream>
#define nmax 2000005
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int ciur(int n) {
int i, j, cnt = 0;
bool A[nmax];
for (i = 2; i <= n; i++)
A[i] = 0;
for (i = 2; i <= n; i++)
if (A[i] == 0) {
cnt++;
for (j = 2 * i; j <= n; j += i)
A[j] = 1;
}
return cnt;
}
int main() {
int n;
fin >> n;
fout << ciur(n) << "\n";
fin.close();
fout.close();
return 0;
}