#include<stdio.h>
#define NM 1000001
int v[NM+1];

int main(){
freopen("operatii.in","r",stdin);
freopen("operatii.out","w",stdout);
int n,i,j,k,nr=0;
scanf("%d",&n);
for(i=1;i<=n;++i) scanf("%d",&v[i]);
i=1;
do{
	while(i<=n&&!v[i]) i++;
	if(i>n) break;
	j=i;
	while(j<n&&v[j]) j++;
	if(!v[j]) j--;
	if(v[i]&&v[j]){
		for(k=i;k<=j;++k) v[k]--;
		nr++;
		}
	}while(i<=n);
printf("%d",nr);
return 0;
}