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# include <iostream>
#include <bitset>
# include <fstream>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
const int dim = 2000002;
int n, s;
bitset <2000005> E;
int main ()
{
fin >> n;
E[0] = 1;
E[1] = 1;
for ( int i = 2; i <= n; ++i)
if (E[i] == 0) {
++s;
for ( int j = i *i; j <= n; j += i)
E[j] = 1;
}
fout << s;
return 0;
}