#include<stdio.h>
#include<algorithm>
typedef unsigned int uint;
typedef unsigned long long ull;
constexpr uint mod{1000000007};
constexpr uint power(uint x,uint y) {
    uint s{1};
    while(y>0) {
        if(y&1) {
            s=ull(s)*x%mod;
        }
        x=ull(x)*x%mod;
        y>>=1;
    }
    return s;
}
constexpr uint plus(const uint &x,const uint &y) {
    if(x+y>=mod) {
        return x+y-mod;
    }
    return x+y;
}
constexpr uint minus(const uint &x,const uint &y) {
    if(x<y) {
        return x-y+mod;
    }
    return x-y;
}
constexpr int N{3000};
uint fac[(N<<1)+5];
uint ipw2[(N<<1)+5];
uint C[N+5][N+5];
int main() {
    int n,m;
    scanf("%d%d",&n,&m);
    if(n>m) {
        std::swap(n,m);
    }
    fac[0]=1;
    for(int i=1;i<=n<<1;i++) {
        fac[i]=ull(fac[i-1])*i%mod;
    }
    ipw2[0]=1;
    for(int i=1;i<=n+m;i++) {
        ipw2[i]=ull(ipw2[i-1])*power(2,mod-2)%mod;
    }
    C[0][0]=1;
    for(int i=1;i<=m;i++) {
        C[i][0]=C[i][i]=1;
        for(int j=1;j<i;j++) {
            C[i][j]=plus(C[i-1][j-1],C[i-1][j]);
        }
    }
    const auto calc([&](const int &n,const int &m)->uint {
        uint res{0};
        for(int i=m;i<=n<<1;i++) {
            res=(res+ull(fac[i])*C[n][i-n]%mod*C[m][i-m]%mod*ipw2[(i-m)+(i-n)])%mod;
        }
        return res;
    });
    uint ans{0};
    for(int i=0;i<=n;i++) {
        ans=(ans+ull(i&1?mod-fac[i]:fac[i])*C[n][i]%mod*C[m][i]%mod*calc(n-i,m-i)%mod*ipw2[i])%mod;
    }
    printf("%u\n",ans);
    return 0;
}