#include <cstdio>
const int N = 1e6 + 10;
int primes[N], cnt;
bool st[N];
void get_primes(int n)
{
for (int i = 2; i <= n; i ++ )
{
if (!st[i])
{
primes[cnt ++ ] = i; //primes用于存放筛出来的质数,题目不要求,其实可以不用primes数组
for (int j = i + i; j <= n; j += i) st[j] = true;
}
}
}
int main()
{
int n;
scanf("%d", &n);
get_primes(n);
printf("%d\n", cnt);
return 0;
}