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