蒟蒻萌新刚学OI，求助！

#include<iostream>
#include<cmath>
#include<cstring>
#include<cstdio>
#define MAXN 4
using namespace std;
typedef long long ll;
ll MOD;
ll n;
struct matrix
{
    ll a[MAXN][MAXN];
    matrix(){memset(a,0,sizeof(a));};
}a,b;
matrix operator * (const matrix &x,const matrix &y)
{
    matrix z;
    for (int i=0;i<3;i++)
        for (int j=0;j<3;j++)
            for (int k=0;k<3;k++)
                z.a[i][j]+=x.a[i][k]*y.a[k][j],z.a[i][j]%=MOD;
    return z;
}
void ksm(int p)
{
    while(p)
    {
        if (p&1)
            a=a*b;
        b=b*b;
        p>>=1;
    }
}
int main()
{
	ll flag=0;
    scanf("%lld%lld",&n,&MOD);
    a.a[0][1]=a.a[0][2]=1;
    for (ll t=10;flag<n;t=t*10)
    {
    	b.a[1][0]=b.a[1][1]=b.a[2][1]=b.a[2][2]=1;
        b.a[0][1]=b.a[0][2]=b.a[1][2]=b.a[2][0]=0;
        b.a[0][0]=t%MOD;
        ll p=min(t-1,n)-flag;
        ksm(p);
        flag=min(n,t-1);
	}
	printf("%lld\n",a.a[0][0]);
    return 0;
}