#include<stdio.h>
int main(void){
	int n,i,k,b;
	int a[10086];
	while(scanf("%d",&n)!=EOF){
		k=b=0;
		for(i=0;i<n;i++){
			scanf("%d",&a[i]);
			if(a[i]>0)
			  a[i]=a[i]/2;
			k=k+a[i];
			if(k<0)
			  b=b+1;
		}
		printf("%d\n",b);
	}
	return 0;
}