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