30分，剩下为re。```
#include
using namespace std;
int a[20001],b[20001];
int main()
{
int n;
double a1=0,b1=0;
cin>>n;
for(int i=0;i<n;i++)
{cin>>a[i]>>b[i];
a1+=a[i];
b1+=b[i];}
int shi=(a1+b1)/2*10;
if(shi%10==0) {int jz=(a1+b1)/2;
cout<<jz;}
else
{int jz1=(a1+b1)/2+1;
cout<<jz1;}
return 0;
}
