本人是蒟蒻，此方法为某位大神分享。

#include<bits/stdc++.h>
using namespace std;
const int N = 1e7,mod = 1e9+7;
int n,a,b,c,dp[N];
int main () {
	cin >> n >> a >> b >> c;
	for (int i = 0;i <= c;i++){
		dp[i] = 1;
	}
	for (int i = c+1;i <= n;i++){
		dp[i] = (dp[max(0,i-a)]+dp[max(0,i-b)])
        %mod;
	}
	cout << dp[n];
	return 0;
}