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#include <fstream>
#include <bitset>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
bitset <20000001> p;
int n;
void Eratostene(){
p[0] = p[1] = 1;
for(int i = 2; i <= 1415; ++i)
if(p[i] == 0)
for(int j = 2; i * j <= 2000000; ++j)
p[i * j] = 1;
}
int main(){
cin >> n;
Eratostene();
int cnt = 0;
for(int i = 1; i <= n; ++i)
if(!p[i])
cnt++;
cout << cnt;
return 0;
}