如题，WA了第四个点，求调[doge]

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <ctime>
#include <iomanip>
#include <vector>
#include <queue>

namespace fastIO {
	inline int read() {
		int res = 0, f = 1;
		char ch = getchar();
		while( !(ch >= '0' && ch <= '9') ) {
			if(ch == '-') f = -1;
			ch = getchar();
		}
		while(ch >= '0' && ch <= '9') {
			res = (res << 1) + (res << 3) + (ch ^ 48);
			ch = getchar();
		}
		return res * f;
	}

	void write(int x) {
		static int sta[35];
		int top = 0;
		do {
			sta[top++] = x % 10;
			x /= 10;
		} while(x);
		while(top) putchar(sta[--top] ^ 48);
	}

	void writeln(int x) {
		write(x);
		putchar('\n');
	}
}

using namespace std;
using namespace fastIO;

int A, B; 
int n = 1;
const int maxn = 5;
int a[maxn];
int t[maxn * 4];
#define lson u << 1
#define rson (u << 1) + 1
void pushup(int u) { t[u] = t[lson] * t[rson]; }
void build(int u, int l, int r) {
	if(l == r) t[u] = a[l];
	else {
		int mid = (l + r) / 2;
		build(lson, l, mid);
		build(rson, mid + 1, r);
		pushup(u);
	}
}

void modify(int u, int l, int r, int x ,int y) {
	if(l == r) t[u] *= y;
	else {
		int mid = (l + r) / 2;
		if(x > mid) modify(rson, mid + 1, r, x, y);
		else modify(lson, l, mid, x, y);
		pushup(u);
	} 
}

int sum(int u, int l, int r, int x, int y) {
	if(l == x && r == y) return t[u];
	int mid = (l + r) / 2;
	if(y <= mid) return sum(lson, l, mid, x, y);
	else if(x > mid) return sum(rson, mid + 1, r, x, y);
	else return sum(lson, l, mid, x, mid) * sum(rson, mid + 1, r, mid + 1, y);
}


int main() {

	cin >> a[1] >> B;
	build(1, 1, n);
	modify(1, 1, n, 1, B);
	cout << sum(1, 1, n, 1, 1);
//	printf("\n");
//	cout<<"The time used: ";
//	printf("%.2lfs",(double)clock()/CLOCKS_PER_SEC);

	return 0;

}