#include<stdio.h>
int v[1000000];
int main()
{
	int nr=0,n,rnk=0,nro=0;
	freopen("operatii.in","r",stdin);
	freopen("operatii.out","w",stdout);
	scanf("%d",&n);
	int put=1;
	for(int i=0;i<n;++i)
	{
		scanf("%d",v+i);
		if(!v[i])
			if(!put)
				{
					nr+=nro;
					put=1;
					rnk=0;
					nro=0;
			    }
		if(v[i])
			{
				if(i)
					rnk=v[i-1];
				if(v[i]>rnk)
					nro+=v[i]-rnk;
				put=0;
		    }
	}
	if(v[n-1])
		nr+=nro;
	printf("%d",nr);
	
	return 0;
}