#P38A. Army
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ID: 523
Type: Default
1000ms
256MiB
Tried: 0
Accepted: 0
Difficulty: (None)
Uploaded By:
Hydro
Tags> Army
Description
The Berland Armed Forces System consists of n ranks that are numbered using natural numbers from 1 to n, where 1 is the lowest rank and n is the highest rank.
One needs exactly di years to rise from rank i to rank i + 1. Reaching a certain rank i having not reached all the previous i - 1 ranks is impossible.
Vasya has just reached a new rank of a, but he dreams of holding the rank of b. Find for how many more years Vasya should serve in the army until he can finally realize his dream.
The first input line contains an integer n (2 ≤ n ≤ 100). The second line contains n - 1 integers di (1 ≤ di ≤ 100). The third input line contains two integers a and b (1 ≤ a < b ≤ n). The numbers on the lines are space-separated.
Print the single number which is the number of years that Vasya needs to rise from rank a to rank b.
Input
The first input line contains an integer n (2 ≤ n ≤ 100). The second line contains n - 1 integers di (1 ≤ di ≤ 100). The third input line contains two integers a and b (1 ≤ a < b ≤ n). The numbers on the lines are space-separated.
Output
Print the single number which is the number of years that Vasya needs to rise from rank a to rank b.
题目描述
在北爱尔兰军队的行政系统中有 n 个军衔，其中 1 最低，n 最高。
你需要di年来从 i 级升到 i+1 级。在你升到 i 级时必须已经到达前面所有等级。
Vasya 刚刚达到 a 级，但他想达到 b 级。请问他至少还要再参军多少年。
输入格式
第一行：n（2≤n≤100）；
第二行：d1, d2, d3...dn-1 (1<= di <=100)
第三行：a,b（1<=a<b<=n）。
输出格式
仅一行：从 a 级升到 b 级所需的年数。
Samples
3
5 6
1 2
5
3
5 6
1 3
11
