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Problem 3284. -- 不等式

3284: 不等式

Time Limit: 3 Sec  Memory Limit: 256 MB
Submit: 44  Solved: 26
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Description

有M个未各数X1,X2....Xm,求满足以下条件不等式的
正整数解
1:1<=i<=N,Xi<=t
2:X1+X2+...+Xm<=s

Input

一行四个数S,T,N,M
S<=10^18,N<=10^9,N*T<=S,m-n<=1000

Output

输出方案数Mod 10^9+7

Sample Input

5 2 2 3

Sample Output

8

HINT

Source

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