POJ 2393

 1 #include <iostream>
 2 #include <algorithm>
 3 using namespace std;
 4 
 5 int main()
 6 {
 7     //freopen("acm.acm","r",stdin);
 8     long long n;
 9     long long s;
10     long long pre_per;
11     long long pre_cap;
12     long long cur_per;
13     long long cur_cap;
14     long long sum;
15     cin>>n;
16     cin>>s;
17     cin>>pre_per;
18     cin>>pre_cap;
19     sum = 0;
20     sum += pre_per*pre_cap;
21     while(cin>>cur_per>>cur_cap)
22     {
23         if(pre_per*cur_cap + s*cur_cap < cur_per*cur_cap)
24         {
25             sum += pre_per*cur_cap + s*cur_cap;
26         }
27         else
28         {
29             sum += cur_per*cur_cap;
30         }
31         pre_per = cur_per;
32         pre_cap = cur_cap;
33     }
34     cout<<sum<<endl;
35 }