#include <stdio.h>

/* 2進数の乗算 */
unsigned long multiply(unsigned short a, unsigned short b)
{
    unsigned long x, y, z = 0;
    int i;
    x = a;
    y = b;
    for (i = 1; i <= 16; i++) {
        if (y & 1 == 1) z += x;
        x <<= 1;
        y >>= 1;
    }
    return z;
}

/* メイン ルーチン */
int main()
{
    unsigned short x, y;
    unsigned long z;

    printf("正の整数を入力：");
    scanf("%u %u", &x, &y);
    z = multiply(x, y);
    printf("%u x %u = %lu\n", x, y, z);

    return 0;
}