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