#include<stdio.h>
FILE*f=fopen("operatii.in","r");
FILE*g=fopen("operatii.out","w");
long a[1000004];
long n;
void read()
	{
	long i,j;
	fscanf(f,"%ld",&n);
	for(i=1;i<=n;++i) fscanf(f,"%ld",&a[i]);
	}
void solve()
	{
	int ok=0;
	long long unsigned sol=0;
	long i,j;
	do
		{
		ok=1;
		for(i=1;i<=n&&ok==1;++i)
			{
			j=i;
			if(a[j]>0&&ok==1) {sol++;  ok=0;
			while(j<=n&&a[j]!=0)
				{
				a[j]--;
				j++;

			}   break; }
			}
		}
	while(ok==0);
	fprintf(g,"%llu",sol);
	}
int main()
	{
	read();
	solve();
	return 0;
	}