#include<bits/stdc++.h>
#define int long long
#define db double
#define maxn 1000005
#define mod 1000000007
#define fir first
#define sec second
#define pr pair<int,int>
#define mk make_pair
#define inf 10000000000000000
using namespace std;
inline int read()
{
    int SS=0,WW=1;
    char ch=getchar();
    while(ch<'0'||ch>'9')
	{
        if(ch=='-')WW=-1;
        ch = getchar();
    }
    while(ch>='0'&&ch<='9')
	{
        SS=(SS<<1)+(SS<<3)+(ch^48);
        ch=getchar();
    }
    return SS*WW;
}
inline void write(int XX)
{
    if(XX<0)putchar('-'),XX=-XX;
    if(XX>9)write(XX/10);
    putchar(XX% 10 + '0');
}
int n,fx[maxn],fy[maxn],lx=1e9,ly=1e9,rx,ry,ans;
bool f[2005][2005];
bool cha(int x,int y,int X,int Y)
{
	return x*Y-X*y>=0;
}
bool check(int x,int y)
{
	for(int i=1;i<=n;i++)
		if(!cha(fy[i+1]-fy[i],fx[i+1]-fx[i],y-fy[i],x-fx[i]))return false;
	return true;
}
bool ck(int x,int y)
{
	if(x>=lx&&x<=rx&&y>=ly&&y<=ry&&f[x][y])return true;
	return false;
}
signed main()
{
	n=read();
	for(int i=1;i<=n;i++)fx[i]=read(),fy[i]=read(),lx=min(lx,fx[i]),rx=max(rx,fx[i]),ly=min(ly,fy[i]),ry=max(ry,fy[i]);
	fx[n+1]=fx[1],fy[n+1]=fy[1];
	for(int i=lx;i<=rx;i++)
		for(int j=ly;j<=ry;j++)f[i][j]=check(i,j);
	for(int i=lx;i<=rx;i++)
		for(int j=ly;j<=ry;j++)
		{
			if(!f[i][j])continue;
			for(int k=i;k<=rx;k++)
				for(int p=j+1;p<=ry;p++)
					if(f[k][p]&&ck(k-p+j,p+k-i)&&ck(i-p+j,j+k-i))
						ans++;
		}
	write(ans);
	return 0;
}