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 }
