/**
 *   Author: aksayushx
**/
#include<bits/stdc++.h>
#define F       first
#define S       second
#define all(a)  a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define sz(x)   (long long)x.size()
#define uniq(a) a.erase(unique(all(a)),a.end())
#define pb      push_back
#define mp      make_pair
#define mod     1'000'000'007
#define MOD     998244353
#define pi      3.141592653589793238462
#define pll     pair<ll,ll>
#define pii     pair<int,int>
#define setp(x) fixed<<setprecision(x)
#define deb(x)  cerr<<#x<<"="<<x<< '\n'
using namespace std;
typedef long long ll;
typedef long double ld;



ll power(ll x,ll y,ll m);
ll modInverse(ll n,ll m);
ll nCr(ll n,ll r,ll m);
ll ceiling(ll x,ll y);

const int block=700;
const double eps=1e-9;
const int rnd_mx=1e9;

template <typename T>
void read(vector<T>& a){
    for(T &e:a){
        cin>>e;
    }
}

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

inline bool equal(ld x,ld y){
    return abs(x-y)<eps;
}


void add(int& a,int b){
    a+=b;
    if(a>=MOD) a-=MOD;
}

int lcm(int a,int b){
    return (a*b)/__gcd(a,b);
}


const int mx=3000;

struct fenwick{
    int n;
    vector<int> bit;
    fenwick(int n){
        this->n=n;
        bit.assign(n,0);
    }
    int sum(int r){
        int s=0;
        for(;r>=0;r=(r&(r+1))-1){
            s=(s+bit[r])%mod;
        }
        return s;
    }
    void update(int idx,int del){
        for(;idx<n;idx=idx|(idx+1)){
            bit[idx]=(bit[idx]+del)%mod;
        }
    }
};


void aksayushx()
{
    int n,m;
    cin>>n>>m;
    vector<int> a(n),b(m);
    read(a),read(b);
    auto ac=a;
    uniq(ac);
    sort(all(ac));
    int acs=ac.size();
    vector<vector<int>> dp(m,vector<int>(n,0));

    function<int(int)> idx=[&](int x){
        int idx=lower_bound(all(ac),x)-ac.begin();
        return idx;
    };

    fenwick ft(acs);

    for(int i=0;i<n;i++){
        dp[0][i]=1;
    }

    for(int i=1;i<m;i++){
        ft=fenwick(acs);
        for(int j=0;j<n;j++){
            int val=b[i]+a[j],xt=val-b[i-1];

            if(j>0) ft.update(idx(a[j-1]),dp[i-1][j-1]);

            if(xt<=0) continue;
            int id=upper_bound(all(ac),xt)-ac.begin();

            --id;
            if(id<0) continue;
            dp[i][j]=(dp[i][j]+ft.sum(id))%mod;
        }
    }
    int ans=0;
    for(int i=0;i<n;i++){
        ans+=dp[m-1][i];
        ans%=mod;
    }
    cout<<ans<<'\n';
}


int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    #ifdef AKSAYUSHX
    (void)!freopen("input.txt","r",stdin);
    (void)!freopen("output.txt","w",stdout);
    (void)!freopen("error.txt","w",stderr);
    #endif
    int t=1,x=1;
    //cin>>t;
    while(t--)
    {
        //cout<<"Case #"<<x++<<": ";
        aksayushx();
    }
    return 0;
}


// Returns x raised to the power y modulo mod
ll power(ll x, ll y, ll m=mod)
{
    ll res = 1;
    x = x % m;
    if (x == 0) return 0;
    while (y > 0)
    {
        if (y & 1)
            res = (res*x) % m;
        y = y>>1;
        x = (x*x) % m;
    }
    return res;
}

ll modInverse(ll n,ll m=mod)
{
    return power(n, m-2,m);
}

ll ceiling(ll x,ll y)
{
    return (x+y-1)/y;
}

/*
ll nCr(ll n,ll r,ll m=mod)
{
    if(r==0) return 1;
    //return (fac[n] * minv[r] % m * minv[n - r] % m) % m;
    return (fac[n] * modInverse(fac[r],m) % m * modInverse(fac[n - r],m) % m) % m;
}*/