#include<stdio.h>
int main()
{   int n,m;
     float sum1,sum2;
 while(scanf("%d",&n) != EOF){
      sum1 = 0;
        sum2 = 0; 
    while(n--){
        m = 0;
    	scanf("%d",&m);
    	if(m>0){ 
    	   sum1 += m/2.0;
		} else if(m<0){
		  sum1 = sum1+m;
       	}
		if(sum1<0){
    		sum2 += 1;
		}
	}
	printf("%g\n",sum2);
}
	return 0;
}