#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <string.h>
using namespace std;
const int mod = 1000000007;
int dp[2][2][505];
int main() {
int n, a, b;
while(cin >> n >> a >> b) {
int now, pre;
dp[0][0][0] = dp[0][1][0] = 1;
for (int i = 1; i <= n; ++i) {
now = i & 1;
pre = (i-1) & 1;
memset(dp[now], 0, sizeof(dp));//滚动数组 now 位置记得清零
for (int j = 1; j <= a; ++j) {
dp[now][0][j] += dp[pre][0][j-1];
if (dp[now][0][j] >= mod)
dp[now][0][j] -= mod;
dp[now][1][1] += dp[pre][0][j];
if (dp[now][1][1] >= mod)
dp[now][1][1] -= mod;
}
for (int j = 1; j <= b; ++j) {
dp[now][1][j] += dp[pre][1][j-1];
if (dp[now][1][j] >= mod)
dp[now][1][j] -= mod;
dp[now][0][1] += dp[pre][1][j];
if (dp[now][0][1] >= mod)
dp[now][0][1] -= mod;
}
}
int ans = 0;
for (int i = 1; i <= a; ++i) {
ans += dp[n&1][0][i];
if (ans >= mod)
ans -= mod;
}
for (int i = 1; i <= b; ++i) {
ans += dp[n&1][1][i];
if (ans >= mod)
ans -= mod;
}
cout << ans << endl;
}
}