#include<stdio.h>
int main(){
int n,a,i,b;
int fei[1000];
while(scanf("%d",&n)!=EOF){
	a=0;
	b=0;
	for(i=0;i<n;i++){
		scanf("%d",&fei[i]);
		if(fei[i]>0)
		a+=(fei[i]/2);
		else
			a+=fei[i];
		if(a<0)
			b+=1;}
	printf("%d\n",b);}
	

}