#include<iostream> using namespace std; int main(){ int a,b[100],c=0; cin>>a; for(int i=0;i<=a;i++){ cin>>b[i]; } for(int i=0;i<=a;i++){ if(b[i]-b[i+1]==1||b[i]-b[i+1]==2){ c++; } } cout<<c; }