有点不理解

#include <bits/stdc++.h>
#define ll long long
using namespace std;
unsigned ll a,b,c; 
int main(){
	cin >> a >> b;
	c=a;
	if(a==1){
		cout << 1;
		return 0;
	} 
	for(ll i=1;i<b-1;i++){
		c=a*c;
	}
	if(c<=1000000000){
		cout << c;
	}else{
		cout << -1;
	}
	return 0;
}