from copy import copy

N=int(input())
Y=[0]+list(map(int,input().split()))+[10**10]
Z=copy(Y)

for i in range(N+1):
    if Z[i]>Z[i+1]:
        while Z[i]>Z[i+1]:
            Z[i+1]+=1
            if Z[i-1]<Z[i]:
                Z[i]-=1

C=0
for i in range(1,N+1):
    C+=abs(Y[i]-Z[i])
print(C)