#include <iostream>
#include <cstdio>
#define nmax 2000005

using namespace std;

int n,nr;
bool prim[nmax];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    cin>>n;
    for(int i=2;i*i<=n;i++)
        if(prim[i]==0)
            for(int j=i*i;j<=n;j+=i)
                prim[j]=1;
    for(int i=2;i<=n;i++)
        if(prim[i]==0)
            nr++;
    cout<<nr;
    return 0;
}