炒股

https://ac.nowcoder.com/acm/contest/625/I 

思路：先拿第一张，如果当前的价格对与手上的能转就交换，如果低于手上的就相当于抛弃手上的买当前的（想成前面的没买而是买现在）；

#include<algorithm>
#include<set>
#include<vector>
#include<queue>
#include<cmath>
#include<cstring>
#include<iostream>
#include<set>
#include<vector>
#include<queue>
#include<cmath>
#include<cstdio>
#include<map>
#include<stack>
#include<string>
using namespace std;

#define sfi(i) scanf("%d",&i)
#define pri(i) printf("%d\n",i)
#define sff(i) scanf("%lf",&i)
#define ll long long
#define mem(x) memset(x,0,sizeof(x))
#define INF 0x3f3f3f3f
#define eps 1e-16
#define PI acos(-1)
#define lowbit(x) ((x)&(-x))
#define zero(x) (((x)>0?(x):-(x))<eps)
#define fl() printf("flag\n")
#define MOD(x) ((x%mod)+mod)%mod
#define endl '\n'
#define FAST_IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
ll gcd(ll a,ll b){while(b^=a^=b^=a%=b);return a;}
const int maxn=5e5+9;
const int mod=1e9+7;

template <class T>
inline void sc(T &ret)
{
    char c;
    ret = 0;
    while ((c = getchar()) < '0' || c > '9');
    while (c >= '0' && c <= '9')
    {
        ret = ret * 10 + (c - '0'), c = getchar();
    }
}

int a[maxn];
int main()
{
    //FAST_IO;
    int n;
    cin>>n;
    for(int i=0;i<n;i++) cin>>a[i];
    int now=a[0];
    ll ans=0;
    for(int i=1;i<n;i++)
    {
        if(a[i]>now)
        {
            ans=ans+a[i]-now;
            now=a[i];
        }
        else
        {
            now=a[i];
        }
    }
    cout<<ans<<endl;
    return 0;
}