参考讲解
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int N = 100010;
int nums[N];
int main(){
int n;
cin >> n;
for(int i = 0; i < n; i++){
cin >> nums[i];
}
int sum = 0;
for(int i = 0; i < n-1; i++){
sum += max(0, nums[i+1] - nums[i]);
}
printf("%d\n", sum);
return 0;
}