1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
#include <iostream>
#include <vector>

using namespace std;

int main(){

    int n, sum1 = 0, sum2 = 0;
    int a;
    int tab[50000], kopia[50000];


    cin >> n;
    for(int i = 0; i < n; i++){
        cin >> a;
        tab[i] = a;
        kopia[i] = a;
    }

    for(int i = 1; i < n; i++){
        if(i % 2 == 1){
            if(i+1 < n){
                if(tab[i] <= tab[i-1]){
                    if(tab[i-1] >= tab[i+1])
                        tab[i] = tab[i-1]+1;
                    else
                        tab[i] = tab[i+1]+1;
                    sum1++;
                }
            }
            else{
                if(tab[i] <= tab[i-1]){
                    tab[i] = tab[i-1]+1;
                    sum1++;
                }
            }
        }
        else{
            if(i+1 < n){
                if(tab[i] >= tab[i-1]){
                    if(tab[i-1] >= tab[i+1])
                        tab[i] = tab[i+1]-1;
                    else
                        tab[i] = tab[i-1]-1;
                    sum1++;
                }
            }
            else{
                if(tab[i] >= tab[i-1]){
                    tab[i] = tab[i-1]-1;
                    sum1++;
                }
            }
        }
    }
    
    for(int i = 1; i < n; i++){
        if(i % 2 == 0){
            if(i+1 < n){
                if(kopia[i] <= kopia[i-1]){
                    if(kopia[i-1] >= kopia[i+1])
                        kopia[i] = kopia[i-1]+1;
                    else
                        kopia[i] = kopia[i+1]+1;
                    sum2++;
                }
            }
            else{
                if(kopia[i] <= kopia[i-1]){
                    kopia[i] = kopia[i-1]+1;
                    sum2++;
                }
            }
        }
        else{
            if(i+1 < n){
                if(kopia[i] >= kopia[i-1]){
                    if(kopia[i-1] >= kopia[i+1])
                        kopia[i] = kopia[i+1]-1;
                    else
                        kopia[i] = kopia[i-1]-1;
                    sum2++;
                }
            }
            else{
                if(kopia[i] >= kopia[i-1]){
                    kopia[i] = kopia[i-1]-1;
                    sum2++;
                }
            }
        }
    }

    if(sum1 >= sum2)
        cout << sum2 << endl;
    else
        cout << sum1 << endl;

    return 0;
}