HDU 1163 Eddy's digital Roots 水题

#include<cstdio>
#include<cstring>
int n, sum, p;
void gao(int &sum, int &p)
{
    while(sum >= 10)
    {    
        p = 0;
        while(sum)
            p += sum % 10, 
            sum /= 10;
        sum = p;
    }
}
int main()
{
    int i, j;
    while( ~scanf("%d", &n) && n)
    {
        sum = 1; 
        for(i = 1; i <= n; i++)
            sum *= n, gao(sum, p); 
        gao(sum, p);
        printf("%d\n", sum);
    }
    return 0;
}