C++ :

#include<cstdio>
#define LL long long
LL n,m,t,p;
LL x[202],y[202];
namespace A
{
          LL f[200001];
          LL ans[202];
          LL power(LL x,LL n)
          {
             LL t;
             if (n==0) return 1;
             t=power(x,n/2);
             if (n%2==0) return (t*t)%p;
             else return (((t*t)%p)*x)%p;
          }
          LL count(LL x,LL y)
          {
             return (f[x+y]*power((f[x]*f[y])%p,p-2))%p;
          }
          void solve()
          {
               int i,j;
               f[0]=1;
               for (i=1;i<=n+m;i++) f[i]=(f[i-1]*i)%p;
               for (i=1;i<=t;i++)
               {
                   ans[i]=count(x[i],y[i]);
                   for (j=1;j<=i-1;j++)
                       if (y[j]<=y[i]) ans[i]=(ans[i]+p-(ans[j]*count(x[i]-x[j],y[i]-y[j])%p))%p;
               }
               printf("%lld\n",ans[t]);
          }
}
namespace B
{
          const LL pp[4]={3,5,6793,10007};
          LL fac[4][10007];
          LL ans[202];
          LL power(LL a,LL b,LL p)
          {
             LL c;
             if (b==0) return 1;
             c=power(a,b/2,p);
             if (b%2==0) return (c*c)%p;
             else return (((c*c)%p)*a)%p;
          }
          LL f1(LL x,LL p)
          {
             LL pp,ans;
             pp=p; ans=0;
             while (x/pp>0)
             {
                   ans+=x/pp; pp*=p;
             }
             return ans;
          }
          LL f2(LL x,int i)
          {
             LL ans;
             ans=1;
             while (x>0)
             {
                   if ((x/pp[i])%2==1) ans=(ans*(-fac[i][x%pp[i]]+pp[i])%pp[i])%pp[i];
                   else ans=(ans*fac[i][x%pp[i]])%pp[i];
                   x/=pp[i];
             }
             return ans;
          }
          LL count(LL x,LL y)
          {
             LL dx,ex;
             int i;
             ex=0;
             for (i=0;i<=3;i++)
             {
                 if (f1(x+y,pp[i])-f1(x,pp[i])-f1(y,pp[i])>0) dx=0;
                 else dx=(f2(x+y,i)*power((f2(x,i)*f2(y,i))%pp[i],pp[i]-2,pp[i]))%pp[i];
                 ex=(ex+(((p/pp[i]*dx)%p)*power(p/pp[i],pp[i]-2,pp[i]))%p)%p;
             }
             return ex;
          }
          void solve()
          {
               int i,j;
               for (i=0;i<=3;i++)
               {
                   fac[i][0]=1;
                   for (j=1;j<=pp[i]-1;j++) fac[i][j]=(fac[i][j-1]*j)%pp[i];
               }
               for (i=1;i<=t;i++)
               {
                   ans[i]=count(x[i],y[i]);
                   for (j=1;j<=i-1;j++)
                       if (y[j]<=y[i]) ans[i]=(ans[i]+p-(ans[j]*count(x[i]-x[j],y[i]-y[j])%p))%p;
               }
               printf("%lld\n",ans[t]);
          }
}
int main()
{
    LL i,j,temp;
   // freopen("path.in","r",stdin);
   // freopen("path.out","w",stdout);
    scanf("%lld%lld%lld%lld",&n,&m,&t,&p);
    for (i=1;i<=t;i++) scanf("%d%d",&x[i],&y[i]);
    t++; x[t]=n; y[t]=m;
    for (i=1;i<=t-1;i++)
        for (j=i+1;j<=t;j++)
            if ((x[i]>x[j])||((x[i]==x[j])&&(y[i]>y[j])))
            {
               temp=x[i]; x[i]=x[j]; x[j]=temp;
               temp=y[i]; y[i]=y[j]; y[j]=temp;
            }
    if (p==1000003) A::solve();
    else B::solve();
    return 0;
}