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