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