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#include <iostream>
using namespace std;

int main(){
    // Jakub Wasilewski (nazwa konta rekrer)
    int length;
    cin >> length;
    int digits[50001];
    for(int i = 1; i <= length; i++){
        cin >> digits[i];
    }
    int err1 = 0;
    int errLen = 0;

    if(digits[1]<digits[1+1]){
        //OK
    }else{
        errLen++;
        //BLAD
    }
    for(int i = 2; i <= length-1; i++){
        if(i%2==0){
            if(digits[i]>digits[i-1]&&digits[i]>digits[i+1]){
                //OK
                if(errLen>0){
                    if(errLen%2==0){
                        err1+= ((errLen)/2);
                    }else{
                        err1+= ((errLen-1)/2);
                    }
                }
                errLen = 0;
            }else{
                errLen++;
                //BLAD
            }
        }else{
            if(digits[i]<digits[i-1]&&digits[i]<digits[i+1]){
                //OK
                if(errLen>0){
                    if(errLen%2==0){
                        err1+= ((errLen)/2);
                    }else{
                        err1+= ((errLen-1)/2);
                    }
                }
                errLen = 0;
            }else{
                errLen++;
                //BLAD
            }
        }
    }
    if(length%2==0){
        if(digits[length]>digits[length-1]){
            //OK
            if(errLen>0){
                if(errLen%2==0){
                    err1+= ((errLen)/2);
                }else{
                    err1+= ((errLen-1)/2);
                }
            }
            errLen = 0;
        }else{
            errLen++;
            //BLAD
        }
    }else{
        if(digits[length]<digits[length-1]){
            //OK
            if(errLen>0){
                if(errLen%2==0){
                    err1+= ((errLen)/2);
                }else{
                    err1+= ((errLen-1)/2);
                }
            }
            errLen = 0;
        }else{
            errLen++;
            //BLAD
        }
    }
    if(errLen>0){
        if(errLen%2==0){
            err1+= ((errLen)/2);
        }else{
            err1+= ((errLen-1)/2);
        }
    }
    errLen = 0;





    int err2 = 0;

    if(digits[1]>digits[1+1]){
        //OK
    }else{
        errLen++;
        //BLAD
    }
    for(int i = 2; i <= length-1; i++){
        if(i%2==1){
            if(digits[i]>digits[i-1]&&digits[i]>digits[i+1]){
                //OK
                if(errLen>0){
                    if(errLen%2==0){
                        err2+= ((errLen)/2);
                    }else{
                        err2+= ((errLen-1)/2);
                    }
                }
                errLen = 0;
            }else{
                errLen++;
                //BLAD
            }
        }else{
            if(digits[i]<digits[i-1]&&digits[i]<digits[i+1]){
                //OK
                if(errLen>0){
                    if(errLen%2==0){
                        err2+= ((errLen)/2);
                    }else{
                        err2+= ((errLen-1)/2);
                    }
                }
                errLen = 0;
            }else{
                errLen++;
                //BLAD
            }
        }
    }
    if(length%2==1){
        if(digits[length]>digits[length-1]){
            //OK
            if(errLen>0){
                if(errLen%2==0){
                    err2+= ((errLen)/2);
                }else{
                    err2+= ((errLen-1)/2);
                }
            }
            errLen = 0;
        }else{
            errLen++;
            //BLAD
        }
    }else{
        if(digits[length]<digits[length-1]){
            //OK
            if(errLen>0){
                if(errLen%2==0){
                    err2+= ((errLen)/2);
                }else{
                    err2+= ((errLen-1)/2);
                }
            }
            errLen = 0;
        }else{
            errLen++;
            //BLAD
        }
    }
    if(errLen>0){
        if(errLen%2==0){
            err2+= ((errLen)/2);
        }else{
            err2+= ((errLen-1)/2);
        }
    }
    if(err1>err2){
        cout << err2<<"  ";
    }else{
        cout << err1;
    }
    return 0;
}