fzu 2238 Daxia & Wzc's problem

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
typedef long long LL;
LL Power_mod(LL a, LL b, LL p)
{
LL res = 1;
while(b!=0)
{
if(b&1) res = (res*a)%p;
a = (a*a)%p;
b >>= 1;
}
return res;
}
LL Comb(LL a,LL b, LL p)
{
if(a < b) return 0;
if(a == b) return 1;
if(b > a-b) b = a-b;
LL ans = 1, ca = 1, cb = 1;
for(LL i=0; i<b; ++i)
{
ca = (ca*(a-i))%p;
cb = (cb*(b-i))%p;
}
ans = (ca*Power_mod(cb, p-2, p))%p;
return ans;
}
LL Lucas(int n, int m, int p)
{
LL ans = 1;
while(n && m && ans)
{
ans = (ans * Comb(n%p, m%p, p))%p;
n /= p;
m /= p;
}
return ans;
}
int main()
{
int a,d,m,i;
while(scanf("%d%d%d%d",&a,&d,&m,&i) !=EOF)
{
long long int ans1=Lucas(i+m-1,m,1000000007)*a%1000000007;
long long int ans2=Lucas(i+m-1,m+1,1000000007)*d%1000000007;
long long int ans=(ans1+ans2)%1000000007;
printf("%lld\n",ans);
}
return 0;
}