#include <cstdio>

using namespace std;
int n,i,pr1,j;
bool pr[20000001];
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    pr1=1;
    for (i=2;i<=n;i+=2)
    {
        pr[i]=true;
    }
    for (i=3;i<=n;i+=2)
    {
        if (pr[i]==false)
        {
            pr1++;
            for (j=i+i;j<=n;j=j+i)
            pr[j]=true;
        }
    }
    printf("%d", pr1);
    return 0;
}