#include <stdio.h>
const long long mod = 1000000007;
long long pow(long long a, long long p)
{
a %= mod;
p = (p % (mod - 1) + mod - 1) % (mod - 1);
long long r = 1;
while (p){
if (p & 1) r = r * a % mod;
a = a * a % mod;
p /= 2;
}
return r;
}
long long inv2[1010],comb[1010][1010];
int main()
{
inv2[0] = 1;
for (int i=1;i<=1000;i++){
inv2[i] = inv2[i-1] * 500000004 % mod;
}
for (int i=0;i<=1000;i++){
comb[i][0] = comb[i][i] = 1;
for (int j=1;j<i;j++) comb[i][j] = (comb[i-1][j-1] + comb[i-1][j]) % mod;
}
int h,w; scanf ("%d %d",&h,&w);
long long ans = 0;
for (int i=1;i<=h;i++) for (int j=1;i+j<=h;j++){
long long coeff = comb[h][i] * comb[h-i][j] % mod;
long long cnt = (pow(inv2[i]+inv2[j]+1,w) - pow(inv2[i]+1,w) - pow(inv2[j]+1,w) + 1 + mod * 2) % mod;
ans = (ans + coeff * cnt) % mod;
}
for (int k=0;k<2;k++){
for (int i=1;i<=h;i++) for (int j=1;i+j<=h;j++){
long long coeff = comb[h][i] * comb[h-i][j] % mod;
long long cnt = (pow(inv2[i+j]+inv2[i]+inv2[j]+1,w) - pow(inv2[i]+inv2[j]+1,w) + mod) % mod;
ans = (ans + coeff * cnt) % mod;
}
int t = h; h = w; w = t;
}
printf ("%lld\n",ans);
return 0;
}
