#include<bits/stdc++.h>
typedef uint64_t u64;
typedef int64_t i64;
using namespace std;

template<u64 mod> struct modint{
  u64 val;
  modint(i64 val_=0):val((val_%i64(mod)+i64(mod))%i64(mod)){}
  modint operator-(){
    return (val==0)?0:mod-val;
  }
  modint operator+(modint rhs){
    return modint(*this)+=rhs;
  }
  modint operator-(modint rhs){
    return modint(*this)-=rhs;
  }
  modint operator*(modint rhs){
    return modint(*this)*=rhs;
  }
  modint operator/(modint rhs){
    return modint(*this)/=rhs;
  }
  modint pow(i64 rhs){
    modint res=1,now=(*this);
    while(rhs){
      res*=((rhs&1)?now:1),now*=now,rhs>>=1;
    }
    return res;
  }
  modint &operator+=(modint rhs){
    val+=rhs.val,val-=((val>=mod)?mod:0);
    return (*this);
  }
  modint &operator-=(modint rhs){
    val+=((val<rhs.val)?mod:0),val-=rhs.val;
    return (*this);
  }
  modint &operator*=(modint rhs){
    val=val*rhs.val%mod;
    return (*this);
  }
  modint &operator/=(modint rhs){
    return (*this)*=rhs.pow(mod-2);
  }
  bool operator==(modint rhs){
    return val==rhs.val;
  }
  bool operator!=(modint rhs){
    return val!=rhs.val;
  }
  friend std::ostream &operator<<(std::ostream& os,modint x){
    return os<<(x.val);
  }
  friend std::istream &operator>>(std::istream& is,modint& x){
    u64 t;
    is>>t,x=t;
    return is;
  }
};

i64 tr(i64 x1,i64 y1,i64 x2,i64 y2,i64 x3,i64 y3){
  x2-=x1,y2-=y1;
  x3-=x1,y3-=y1;
  return std::abs(x2*y3-x3*y2);
}

int main(){
  constexpr u64 mod=1000000007;
  typedef modint<mod> mint;
  i64 N;
  cin>>N;
  vector<i64> X(N),Y(N);
  for(int i=0;i<N;++i){
    cin>>X[i]>>Y[i];
  }
  i64 ans=0;
  for(int j=1;j<N-1;++j){
    ans+=tr(X[0],Y[0],X[j],Y[j],X[j+1],Y[j+1]);
  }
  cout<<ans<<endl;
}