N = int(input())
Y = list(map(int,input().split()))
import sys
if N == 1:
    print(0)
    exit()
A = [Y[i+1] - Y[i] for i in range(N-1)]
ans = 0
if A[0] < 0:
    ans += -A[0]
    A[0] = 0
for i in range(1,len(A)):
    if A[i] >= 0:
        continue
    if A[i-1] > 0:
        if A[i] + A[i-1] >= 0:
            ans += -A[i]
            A[i] = 0
            continue
        else:
            ans += A[i-1]
            A[i] += A[i-1]
    if i == len(A)-1:
        ans += -A[i]
    else:
        ans += -A[i]
        A[i+1] += A[i]
        A[i] = 0
print(ans)