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