#include <cstdio>
using namespace std;
int prime[31252];
int bitsieve(int n) {
    for (int i = 3; i * i <= n; i += 2) {
    if (!(prime[i/64] & (1 << ((i >> 1) & 31))))
    for (int j = i * i, k = i << 1; j <= n; j += k)
        (prime[j/64] |= (1 << ((j >> 1) & 31)));
    }
    int s=1;
    for (int i = 3; i <= n; i += 2)
        if (!(prime[i/64] & (1 << ((i >> 1) & 31)))) s++;
    return s;
}
int main()
{
    int n;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    printf("%d\n",bitsieve(n));
    return 0;
}