为什么运行失败？

#include<bits/stdc++.h>  
using namespace std;
int a[3],b,x,num;
int main(){
    x=0;
    num=0;
    cin>>b;
    for (int i = 1;i<=b;i++){
    	cin>>a[2];
    	if (a[2]>=a[1]){
    		x++;
    		num = max(num,x);
		}
		else{
			x = 1;
			a[1] = a[2];
		}
	}
	cout<<num;
    return 0;
}