#include<stdio.h>
int main (){
	int a,b,c,d,n,count,sum;
	char m;
	while(scanf("%d%",&n)!=EOF){
		count=0;sum=0;
		for(a=0;a<n;a++){
			scanf("%d",&b);
			if(b>0)
				b=b/2.0;
			sum+=b;
			if(sum<0)
				count ++;
		
		
		
		}
	printf("%d\n",count);
	
	
	
	}
	
	
	






return 0;}