number of prime

#include<bits/stdc++.h>
using namespace    std;

#define mx           100005


int seive(int m)
{

    vector<int>prime;
    bool vis[m]={0};

    int x=sqrt((int)m);
    for(int i=3; i<=x; i+=2)
    {
        if(vis[i]==0)
         {
            for(int j=i*i; j<m; j+=2*i)
                vis[j]=1;
        }
    }
    int cnt=1;

    for(int i=3; i<=m; i+=2)
        if(vis[i]==0)
            cnt++;
    return cnt;
}

int main()
{
   #ifndef Brain_FUCK
        freopen("input.txt","r",stdin);
        freopen("out.txt","w",stdout);
    #endif

    int n;
    cin>>n;
    if(n<2)cout<<"0"<<endl;
    else if(n==2)cout<<"1"<<endl;
    else
    {
       cout<<seive(n)<<endl;
    }

}