#include<iostream>
#include<algorithm>

using namespace std;

const int N=1e6+5;
bool vis[N];

int main()
{
    int n;  cin>>n;
    for(int i=2;i<=n/i;i++)if(!vis[i])
        for(int j=i*i;j<=n;j+=i)
            vis[j]=1;
    int ans=0;
    for(int i=2;i<=n;i++)
        if(!vis[i]) ans++;
    printf("%d\n",ans);
    return 0;
}