#include<fstream>
#include<cstdio>

using namespace std;

int prim[2000005];
int n,i,j,x;

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