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