#include #include #include #include #include #include #include #include using namespace std; #define M 2000000000 #define N 100005 int a[N],b[N]; int main() { int n,i,j,g; while(~scanf("%d",&n)) { for(i=1;i<=(n-1)*n/2;i++) { scanf("%d",&a[i]); } g=(a[1]+a[2]-a[n])/2; printf("%d\n",g); for(i=1;i