寻找递增序列

随机生成一个序列从前往后寻找5个数a_i是否满足a₁<a₂<a₃<a₄<a₅

#include<stdio.h>
#define M 2147483647
int Scan()
{
    int res=0,ch,flag=0;
    if((ch=getchar())=='-')
        flag=1;
    else if(ch>='0'&&ch<='9') 
        res = ch - '0';
    while((ch = getchar()) >= '0' && ch <= '9' )
        res = res * 10 + ch - '0';
    return flag ? -res : res;
}
int main()
{
    int a,n,a1,a2,a3,a4,a5;
    while(scanf("%d",&n)!=EOF)
    {
        a1=a2=a3=a4=a5=M;
        while(n--)
        {
            a=Scan();
            if(a<=a1) a1=a;
            else if(a<=a2) a2=a;
            else if(a<=a3) a3=a;
            else if(a<=a4) a4=a;
            else if(a<=a5) a5=a;
        }
        if(a5<M) printf("YES\n");
        else printf("NO\n");
    }
}