#include<bits/stdc++.h>
using namespace std;
int a[3005],b[3005];
int main(){
int n;
double g=0;
scanf ( "%d" ,&n);
for ( int i=1;i<=n;i++){
scanf ( "%d%d" ,&a[i],&b[i]);
}
for ( int i=1;i<=n;i++){
for ( int j=i+1;j<=n;j++){
for ( int k=j+1;k<=n;k++){
double r=((a[i]*b[j]-a[j]*b[i])+(a[j]*b[k]-a[k]*b[j])+(a[k]*b[i]-a[i]*b[k]))/2.0;
g+= abs (r);
}
}
}
printf ( "%.1lf" ,g);
return 0;
}
这是我的代码TLE76