#include <cstdio>
#include <bitset>
using namespace std;
bitset <2000003> v;
int n,sol;
void solve()
{
    sol=1;
    for(int i=4;i<=n;i=i+2) v[i]=true;
    for(int i=3;i*i<=n;i=i+2)
    {
        if(v[i]==false)
        {
            ++sol;
            for(int j=i*i;j<=n;j=j+i) v[j]=true;
        }
    }
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    solve();
    printf("%d",sol);
    return 0;
}