#include <stdio.h>

int v[2];

inline int max (int a, int b) {
    return a > b ? a : b;
}

int main(int argc, const char * argv[]) {
    
    freopen ("operatii.in", "r", stdin);
    freopen ("operatii.out", "w", stdout);
    
    int N, poz = 0;
    long long Ans = 0;
    
    scanf("%d", &N);
    
    for (int i=1; i <= N; ++ i) {
        scanf("%d",&v[poz]);
        Ans += max (0, v[poz] - v[! poz]);
        poz = ! poz;
    }
    
    printf ( "%lld\n", Ans );
    return 0;
}