import sys
def MI(): return map(int,sys.stdin.readline().rstrip().split())


A,B,T = MI()
ans = 10**18
for i in range(min(T//B,A)+2):
    j = (T-B*i+A-1)//A
    if j >= 0:
        ans = min(ans,A*j+B*i)

print(ans)