2018. The Debut Album

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <io.h>
#include <string.h>

using namespace std;

const int N=50001;
const int M=301;
const unsigned int MOD=1000000007;
unsigned int dpa[N];
unsigned int dpb[N];
int main()
{
    //freopen("data.in","r",stdin);
    memset(dpa,0,sizeof(dpa));
    memset(dpb,0,sizeof(dpb));
    int n,a,b;
    cin>>n>>a>>b;
    dpa[0]=dpb[0]=1;
    for(int i=1;i<=n;++i)
    {
        for(int j=1;j<=a&&j<=i;++j)
        {
            dpa[i]=(dpa[i]+dpb[i-j])%MOD;
        }
        for(int j=1;j<=b&&j<=i;++j)
        {
            dpb[i]=(dpb[i]+dpa[i-j])%MOD;
        }
    }
    cout<<((dpa[n]+dpb[n])%MOD)<<endl;
    return 0;
}