A, B, T = map(int, input().split())
i = 0
ans = 10**18

while True:
    if i>=A:
        break
    
    if i*B>T:
        ans = min(ans, i*B)
        break
    
    j = (T-i*B+A-1)//A
    ans = min(ans, A*j+B*i)
    i += 1
    
print(ans)