#include <stdio.h>
int main(){
	int n,i,a[10000000],j,x,z;
	while(scanf("%d",&n)!=EOF){
		i=1;x=0;z=0;j=0;
		while(i<=n){
			scanf("%d",&a[i]);
			j=a[i];
			if(j>0)
				x=x+j/2;
			else if(j<0)
				x=x+j;
			if(x<0)
				z=z+1;
			++i;}
		printf("%d\n",z);
	}
	return 0;
}