#include<bits/stdc++.h> using namespace std; #define int long long int read(){int x=0,f=1;char c=getchar();while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}while(c>='0'&&c<='9')x=x*10+c-'0',c=getchar();return x*f;} const int MAXN=100010,Mod=1000000007; int Pow(int x,int y){int rt=1;while(y){if(y&1)rt=rt*x%Mod;x=x*x%Mod,y>>=1;}return rt;} int n,m; void slv(){ n=read(),m=read(); int tmp=Pow(2,m+1)-Pow(2,n); tmp-=(m-n+1)&1?n&1?(m-n+1)/2*3+2:(m-n+1)/2*3+1:(m-n+1)/2*3; tmp=(tmp%Mod+Mod)%Mod*Pow(3,Mod-2)%Mod; printf("%lld",tmp); } signed main(){ slv(); return 0; }