#include <cstdio>

using namespace std;
int n,i,nr = 0;
bool c[2000000];

int main()
{
    int N;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&N);
    for (int i = 2;i * i <= N;++i)
        if (!c[i])
            for (int j = i * i;j <= N;j += i)
                c[j] = true;
    for (int i = 2;i <= N;++i)
        if (!c[i])
            ++nr;
    printf ("%d",nr);
    return 0;
}