CodeForces 768FBarrels and boxes

#include<bits/stdc++.h>using namespace std;const int N=2e5+5,P=1e9+7;int fac[N],ifac[N],inv[N],f,w,h;void pre() {    fac[0]=ifac[0]=inv[1]=1;    for(int i=1;i<N;++i)fac[i]=1ll*i*fac[i-1]%P;    for(int i=2;i<N;++i)inv[i]=1ll*(P-P/i)*inv[P%i]%P;    for(int i=1;i<N;++i)ifac[i]=1ll*inv[i]*ifac[i-1]%P;}int C(int n,int m){    if(m<0||n<m)return 0;    return 1ll*fac[n]*ifac[n-m]%P*ifac[m]%P;}int calc(int r,int b,int k){    if(!b)return 1;    int ans=0;    for(int i=1;i<=r+1&&(!k||i*k<=b);++i){        ans+=1ll*C(r+1,i)*C(b-k*i-1,i-1)%P;        ans%=P;    }return ans;}int pow(int x,int n){    int y=1;    while(n){        if(n&1)y=1ll*y*x%P;        x=1ll*x*x%P;        n>>=1;    }return y;}int Inv(int x){return pow(x,P-2);}int main(){    pre();    scanf("%d %d %d",&f,&w,&h);    int s=calc(f,w,h),d=C(f+w,w);    cout<<1ll*s*Inv(d)%P;}