#include<stdio.h>
#include<string.h>
#define NM 1000001
int v[NM+1];
char s[NM*6+1];

int main(){
freopen("operatii.in","r",stdin);
freopen("operatii.out","w",stdout);
int n,i,j,nr=0,x,l;
char *p;
scanf("%d\n",&n);
fgets(s,NM*6+1,stdin);
l=strlen(s);
s[l]=32,s[l+1]=0;
p=s;i=0;
while(*p){
	x=0;
	while(*p!=32) x=x*10+(*p-48),p++;
	v[++i]=x;
	p++;
	}
i=1;
do{
	while(i<=n&&!v[i]) i++;
	if(i>n) break;
	if(v[i]){
		j=i;
		while(j<=n&&v[j]){
			v[j]--;
			j++;
			}
		nr++;
		}
	}while(i<=n);
printf("%d",nr);
return 0;
}