Tongji Online Judge ID:1011

Tongji Online Judge
Problem 1011: 阶乘末尾非零数求和

#include"stdio.h"
#include"math.h"

#define mask_5(s) ((s<100000)?s:s%100000)
#define mask_6(s) ((s<1000000)?s:s%1000000)

int main()
{
        unsigned int i, j, k, n, num;
        unsigned long sum, sum_every, temp, total;
        while(scanf("%d", &n)!=EOF) {
                sum=1;
                total=0;
                for(i=1; i<=n; i++){
                        sum_every=0;
                        k=i;
                        while(k%10==0) k/=10;
                        while(k!=0) {
                                num=k%10;
                                k/=10;
                                sum_every+=sum*num;
                                if(sum_every%10==0) sum_every/=10;
                                else break;
                        }
                        for(j=1; k!=0; j++) {
                                num=k%10;
                                k/=10;
                                temp=mask_5(sum*num);
                                sum_every+=temp*(int)pow(10, j);
                        }
                        while(sum_every%10==0) sum_every/=10;
                        sum=mask_6(sum_every);
                        total+=sum%10;
                }
                printf("%ld/n", total);
        }
        return 0;
}