zoj2176

容易。

#include <iostream>using namespace std;int main(){    int num;    while(cin >> num && num != -1)    {        int x,y = 0,sum = 0,last_y;        while(num--)        {            last_y = y;            cin >> x >> y;            sum += x*(y - last_y);        }        cout << sum << " miles" << endl;    }    return 0;}