思路：
贪心。
实现：
1 #include <iostream> 2 #include <cstdio> 3 #include <algorithm> 4 using namespace std; 5 typedef long long ll; 6 struct node 7 { 8 ll c, y; 9 }; 10 node a[10005]; 11 ll n, s; 12 13 int main() 14 { 15 cin >> n >> s; 16 for (ll i = 0; i < n; i++) 17 { 18 scanf("%d %d", &a[i].c, &a[i].y); 19 } 20 ll sum = a[0].y * a[0].c; 21 for (ll i = 1; i < n; i++) 22 { 23 sum += min(a[i].c * a[i].y, (a[i - 1].c + s)* a[i].y); 24 } 25 cout << sum << endl; 26 return 0; 27 }