打表发现当m>一定值时，x不变化

#include <iostream>
#include <vector>
#include <set>
using namespace std;
#define int long long
const int mod=1e+7;
signed main() {
    iostream::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
   int x,m;cin>>x>>m;
   x%=10;
   int n=m;
   while((x*x)%10!=x&&m>0){
    x=(x*x)%10;
    m--;
   }
   cout<<x*n<<endl;
    return 0;//AC
 }