import sys
from collections import deque

def main():
    N, *rest = map(int, sys.stdin.read().split())
    A = rest[:N]
    is_peak = [False] * N
    q = deque()
    
    for j in range(1, N-1):
        if A[j-1] < A[j] and A[j] > A[j+1]:
            is_peak[j] = True
            q.append(j)
    
    count = 0
    
    while q:
        j = q.popleft()
        if not is_peak[j]:
            continue
        
        # Perform the operation
        m = min(A[j-1], A[j+1]) - 1
        A[j] = m
        count += 1
        is_peak[j] = False  # This peak is now processed
        
        # Check j-1, j, j+1 for possible new peaks
        for k in [j-1, j, j+1]:
            if 1 <= k <= N-2:
                # Check if k is a peak now
                is_p = (A[k-1] < A[k] and A[k] > A[k+1])
                if is_p:
                    if not is_peak[k]:
                        is_peak[k] = True
                        q.append(k)
                else:
                    if is_peak[k]:
                        is_peak[k] = False  # No longer a peak
    
    print(count)

if __name__ == "__main__":
    main()