#include <bits/stdc++.h>
#define ll long long
#define pii pair<int,int>
using namespace std;
const int MAX=100005;
int N=6;
int A[MAX]={1,2,3,2,1,3};
bool done=false;
int main(){
cin>>N;
for (int i=0;i<N;i++) cin>>A[i];
int ans=0;
while (!done){
vector<int> pos;
pos.push_back(-1);
for (int i=0;i<N;i++) if (A[i]==0) pos.push_back(i);
pos.push_back(N);
for (int i=0;i<pos.size()-1;i++){
int min_v=1<<30;
for (int x=pos[i]+1;x<pos[i+1];x++){
min_v = min(min_v,A[x]);
}
for (int x=pos[i]+1;x<pos[i+1];x++){
A[x]-=min_v;
}
if (min_v!=1<<30){
//cout<<pos[i]<<' '<<pos[i+1]<<' '<<pos.size()<<'\n';
ans++;
}
if (pos.size()==N+2) done=true;
}
}
cout<<ans;
}
