#include<bits/stdc++.h>

typedef int IT;
typedef long long LL;
typedef __int128 int128;
typedef double DB;
typedef long double LDB;

#define pb push_back
#define fst first
#define sec second
#define psh push
#define mkp make_pair
#define PII pair<IT,IT>
#define PLI pair<LL,IT>
#define lowbit(x) ((x)&(-x))
using namespace std;

const int N=2e5+10;

int R;
LL ans;

DB dis(DB x,DB y,DB p,DB q){
    return sqrt((x-y)*(x-y)+(p-q)*(p-q));
}
bool check(int x,int y){
    DB s[4]={dis(0,0,x+0.5,y+0.5),dis(0,0,x+0.5,y-0.5),
        dis(0,0,x-0.5,y+0.5),dis(0,0,x-0.5,y-0.5)};
    for(int i=0;i<4;i++)
        if(s[i]>R) return 0;
    // if(dis(0,0,x+0.5,y+0.5)<=R) return 1;
    return 1;
}

int main(){
    scanf("%d",&R);
    for(int x=0;x<=R;x++){
        int l=0,r=R,res=0;
        while(l<=r){
            int mid=(l+r)>>1;
            if(check(x,mid)) l=mid+1,res=mid;
            else r=mid-1;
        }
        // cout<<res<<endl;
        ans+=res;
    }
    ans=(ans<<2)+1;
    printf("%lld\n",ans);
    return 0;
}

这里二分的 $(x,y)$ 都是正数，感觉思路是对的（？）但是瞪了 $30\min$ 没看出来有啥问题。