#include <stdio.h>

long n;
long a, b;
long long sol;

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

    scanf("%ld", &n); 
    long i;

    scanf("%ld", &a);
    
    sol=a;

    for (i=2; i<=n; ++i)
    {
	if (i&1) scanf("%ld", &a);
	else scanf("%ld", &b);
	if (i&1) 
	    if (a>b) sol+=a-b;
	    else;
	else
	    if (b>a) sol+=b-a;
    }

    printf("%lld", sol);

    return 0;
}