#include<cstdio>
#define nmax 2000005
using namespace std;

int n,count;
char used[nmax];

int main()
{
    int i,j;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d", &n);
    for(i=2; i<=n; ++i)
        used[i]=1;
    for(i=2; i<=n; ++i)
        if(used[i])
        {
            ++count;
            for(j=i+i; j<=n; j+=i)
                used[j]=0;
        }
    printf("%d\n", count);
    return 0;
}