萌新刚学OI,求助大佬

#include<iostream>
#include<cstring>
#include<vector>
#include<cstdio>
using namespace std;
const int mod=998244353;
int n,m,k=2;
vector<int> f1;
vector<int> f2;
int main()
{
    scanf("%d%d",&n,&m);
    for(register int i=1;i<=m;i++)
    {
    	f1.push_back(0);
    	f2.push_back(0);
    }
    f1[1]=1; f1[2]=1; f2[1]=1;
    for(register int i=3;i<=m;i++) f1[i]=(f1[i-1]+f1[i-2])%mod;
    if(n==1)
    {
        printf("%d\n",f2[m]);
        return 0;
    }
    for(register int i=2;i<=m;i++) f2[i]=(f2[i-1]+f1[i])%mod;
    if(n==2)
    {
        printf("%d\n",f2[m]);
        return 0;
    }
    while(k<n)
    {
        swap(f1,f2);
        f2[1]=1;
        for(register int i=2;i<=m;i++)
        {
            f2[i]=(f2[i-1]+f1[i])%mod;
        }
        k++;
    }
    printf("%d\n",f2[m]);
}