Duff is addicted to meat! Malek wants to keep her happy for n days. In order to be happy in i-th day, she needs to eat exactly ai kilograms of meat.
There is a big shop uptown and Malek wants to buy meat for her from there. In i-th day, they sell meat for pi dollars per kilogram. Malek knows all numbers a1, ..., an and p1, ..., pn. In each day, he can buy arbitrary amount of meat, also he can keep some meat he has for the future.
Malek is a little tired from cooking meat, so he asked for your help. Help him to minimize the total money he spends to keep Duff happy forn days.
The first line of input contains integer n (1 ≤ n ≤ 105), the number of days.
In the next n lines, i-th line contains two integers ai and pi (1 ≤ ai, pi ≤ 100), the amount of meat Duff needs and the cost of meat in that day.
Print the minimum money needed to keep Duff happy for n days, in one line.
3
1 3
2 2
3 1
10
3
1 3
2 1
3 2
8
In the first sample case: An optimal way would be to buy 1 kg on the first day, 2 kg on the second day and 3 kg on the third day.
In the second sample case: An optimal way would be to buy 1 kg on the first day and 5 kg (needed meat for the second and third day) on the second day.
做点水题换换脑子。。。
浙大月赛题已经做蒙了QAQ
这题很简单。。
扫的时候记得更新价钱的最小值就好了。
1 /************************************************************************* 2 > File Name: code/cf/#326/A.cpp 3 > Author: 111qqz 4 > Email: rkz2013@126.com 5 > Created Time: 2015年10月22日 星期四 20时00分33秒 6 ************************************************************************/ 7 8 #include<iostream> 9 #include<iomanip> 10 #include<cstdio> 11 #include<algorithm> 12 #include<cmath> 13 #include<cstring> 14 #include<string> 15 #include<map> 16 #include<set> 17 #include<queue> 18 #include<vector> 19 #include<stack> 20 #include<cctype> 21 22 #define yn hez111qqz 23 #define j1 cute111qqz 24 #define ms(a,x) memset(a,x,sizeof(a)) 25 using namespace std; 26 const int dx4[4]={1,0,0,-1}; 27 const int dy4[4]={0,-1,1,0}; 28 typedef long long LL; 29 typedef double DB; 30 const int inf = 0x3f3f3f3f; 31 const int N=1E5+7; 32 int n; 33 int a[N],p[N]; 34 int main() 35 { 36 #ifndef ONLINE_JUDGE 37 freopen("in.txt","r",stdin); 38 #endif 39 40 scanf("%d",&n); 41 for ( int i = 0 ; i < n ; i++) scanf("%d %d",&a[i],&p[i]); 42 int mi = inf; 43 int ans = 0 ; 44 for ( int i = 0 ; i < n ; i++) 45 { 46 if (p[i]<mi) 47 mi = p[i]; 48 49 ans += mi*a[i]; 50 } 51 cout<<ans<<endl; 52 53 54 #ifndef ONLINE_JUDGE 55 fclose(stdin); 56 #endif 57 return 0; 58 }