来了

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

typedef long long ll;
const int mod = 1e9 + 7;

const int maxn = 2e5 + 7;
ll f[maxn],fac[maxn],inv[maxn];

struct P
{
    ll x,y;
}p[maxn];

ll qpow(ll x,ll n)
{
    ll res = 1;
    while(n)
    {
        if(n & 1)
            res = (res * x) % mod;
        x = (x * x) % mod;
        n >>= 1;
    }
    return res;
}

void init()
{
    fac[0] = inv[0] = 1;
    for(int i = 1;i < maxn;i++)
    {
        fac[i] = fac[i - 1] * i % mod;
        inv[i] = qpow(fac[i],mod - 2);
    }
}

ll C(ll n,ll m)
{
    ll s1 = fac[n];
    ll s2 = inv[n - m];
    ll s3 = inv[m];
    return (s1 * s2) % mod * s3 % mod;
}

int cmp(P a,P b)
{
    if(a.x == b.x)return a.y < b.y;
    return a.x < b.x;
}

int main()
{
    init();
    ll h,w,n;
    cin >> h >> w >> n;
    for(int i = 1;i <= n;i++)
    {
        ll x,y;scanf("%lld%lld",&x,&y);
        p[i].x = x;p[i].y = y;
    }
    p[++n].x = h;p[n].y = w;
    sort(p + 1,p + 1 + n,cmp);
    for(int i = 1;i <= n;i++)
    {
        ll res = C(p[i].x + p[i].y - 2,p[i].x - 1);
        for(int j = 1;j < i;j++)
        {
            if(p[j].x > p[i].x || p[j].y > p[i].y)continue;
            res -= f[j] * C(p[i].x - p[j].x + p[i].y - p[j].y,p[i].x - p[j].x);
            res = (res + mod) % mod;
        }
        f[i] = (res + mod) % mod;
    }
    
    printf("%lld\n",f[n]);
    return 0;
}