#include<iostream>
#include<vector>
#include<algorithm>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<ctime>
#include<queue>
#include<set>
#include<map>
#include<stack>
#include<bitset>
using namespace std;
typedef long long LL;
const int N=2010;
int gi() {
int w=0;bool q=1;char c=getchar();
while ((c<'0'||c>'9') && c!='-') c=getchar();
if (c=='-') q=0,c=getchar();
while (c>='0'&&c <= '9') w=w*10+c-'0',c=getchar();
return q? w:-w;
}
vector<int>e[N];
int f[N][N],fa[N],g[N];
int D,T;
const int mod=1e9+7;
inline void dfs(int k,int d) {
if (d>D) D=d,T=k;
for (int t:e[k]) if (t!=fa[k]) fa[t]=k,dfs(t,d+1);
}
inline void dp(int k,int fa,int d) {
if (e[k].size()==1)
for (int i=0;i<=D;i++)
f[k][D+i]=f[k][D-i]=i<=d;
else {
for (int t:e[k]) if (t!=fa) dp(t,k,d-1);
for (int i=0;i<=D*2;i++) {
f[k][i]=1;
for (int t:e[k])
if (t!=fa)
f[k][i]=1LL*f[k][i]*((i?f[t][i-1]:0)+(i==D*2?0:f[t][i+1]))%mod;
}
}
}
int main()
{
int i,k,a,b,n=gi(),ans=0;
for (i=1;i<n;i++) {
a=gi(),b=gi();
e[a].push_back(b);
e[b].push_back(a);
}
D=0;dfs(1,0);
fa[T]=0;D=0;dfs(a=T,0);
if (D&1) {
for (a=T,i=(++D)/=2;i--;a=fa[b=a]);
dp(a,b,D);
dp(b,a,D-1);
for (i=0;i<=D*2;i++) ans=(ans+1LL*f[a][i]*f[b][i+1]+1LL*f[a][i+1]*f[b][i])%mod;
dp(a,b,D-1);
dp(b,a,D);
for (i=0;i<=D*2;i++) ans=(ans+1LL*f[a][i]*f[b][i+1]+1LL*f[a][i+1]*f[b][i])%mod;
dp(a,b,D-1);
dp(b,a,D-1);
for (i=0;i<=D*2;i++) {
ans=(ans-2LL*f[a][i]*f[b][i])%mod;
ans=(ans-1LL*f[a][i]*f[b][i+2])%mod;
ans=(ans-1LL*f[a][i+2]*f[b][i])%mod;
}
if (ans<0) ans+=mod;
} else {
for (k=T,i=D/=2;i--;k=fa[k]);
dp(k,0,D);
for (i=0;i<=D*2;i++) (ans+=f[k][i])%=mod;
}
printf("%d\n",ans);
return 0;
}