#include <stdio.h>

int main(){
	int type = 0;
	scanf("%d",&type);
	
	int num = 0;
	for(int i = 0;i < type;i ++){
		int chair,table;
		scanf("%d%d",&table,&chair);
		
		if(table == 2){
			num += chair;
		}else if(table == 3){
			num += chair * 2;
		}
	}
	printf("%d",num);
}