#include<cstdio>
using namespace std;
int v[2000005];
int ciur(int n)
{
    int nr=1;
    for(int i=3;i<=n;i=i+2)
    {
        if(v[i]==0)
        {
            nr++;
            for(int j=2*i;j<=n;j=j+i)
            {
                v[j]=1;
            }
        }
    }
    return nr;
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n;
    scanf("%d",&n);
    printf("%d",ciur(n));
    return 0;
}