#include<stdio.h>

int main()
{
	int x, N, precedent, operatii = 0;

	freopen("operatii.in", "r", stdin);
	freopen("operatii.out", "w", stdout);

	scanf("%d", &N);

	scanf("%d", &precedent);
	operatii += precedent;

	for(int i = 1; i < N; ++i)
	{
		scanf("%d", &x);
		if(x != 0)
			if(x > precedent)
			{
				operatii += x - precedent;
				precedent = x;
			}
			else
				precedent = x;
		else 
			precedent = x;
	}

	printf("%d\n", operatii);
	return 0;
}