#include<stdio.h>
int main(){
	int n,t,i,m,a1,a2;
	while(scanf("%d",&t)!=EOF){
		a1=0,a2=0;
		for(i=0;i<t;i++){
			scanf("%d",&m);
			if(m>0)
				a1=a1+m/2;
			else
				a1=a1+m;
			if(a1<0)
				a2=a2+1;
		}
		printf("%d\n",a2);
	}
	return 0;
}