题解 | 清楚姐姐买竹鼠

a, b, x = map(int,input().split())
avg_b = b / 3
if avg_b >= a:
    print(a*x)
else:
    results1 = (x // 3 + 1) * b
    results2 = (x // 3) * b + x % 3 * a
    print(min(results1,results2))