#include <bits/stdc++.h>

using namespace std;

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