#include <cstdio>

using namespace std;

bool ciur[2000000];

int main ()
{
    int i, j, n, prim=0;

freopen("ciur.in", "r",stdin);
freopen("ciur.out", "w", stdout);

   scanf("%d",&n);

    for (i = 4; i <= n; i += 2)
        ciur[i] = 1;
    for (i = 3; i <= n; i += 2)
      if (!ciur[i])
        for (j = i + i + i; j <= n; j += i + i)
            ciur[j] = 1;
    for(i = 2; i <=n; i++)
    if(ciur[i]==0)
    prim++;
    printf("%d", prim);
    return 0;
}