#include<bits/stdc++.h>
#define N 100005
using namespace std;
int ans=0,n,a[N];
void dfs(int q){
	if(q>=n+1) return ;
	int i=q,x=q;
	for(i;i<=n;++i){
		if(a[i]<=0) break;
		--a[i];
	}
	while(a[x]==0&&x<=n+5) x++;
	++ans;
	dfs(x);
}
int main(){
	scanf("%d",&n);
	a[n+2]=1;
    for(int i=1;i<=n;++i)scanf("%d",&a[i]);
    dfs(1);
    printf("%d",ans);
	return 0;
}