# include <iostream>
# include <cstring>
using namespace std;
int cur = 0;
bool isp[100000010], prime[100000010];
void getprime()
{
memset(isp, true, sizeof(isp));
isp[0] = isp[1] = false;
for (int i = 2; i <= 10000000; i++)
{
if (isp[i])
{
cur++;
prime[cur] = i;
for (int j = 2; i * j <= 10000000; j++)
{
isp[i * j] = false;
}
}
}
return;
}
int main()
{
getprime();
int n, ans = 0;
cin >> n;
for (int i = 1; i <= cur; i++)
{
if (prime[i] <= n)
ans++;
else
break;
}
cout << ans;
return 0;
}
全WA了用的是线筛