The amount of alcohol in the \(i\)-th liquor is \(V_i*P_i/100\). So one can calculate the sum from the first and output the first index that the sum exceeds \(X\).

However, floating-point operations has errors in some environment. For example, the correct answer for the following input is -1, but some code may output 3, depending on implementations and environments.

3 13
30 13
35 13
35 13

The easiest way to avoid such issue is to apply appropriate transformation to equations so that only integral operations are required.

This time, we want to check if \(V_1*P_1/100+\ldots >X\), so we can multiply \(100\) to both sides to obtain \(V_1*P_1+\ldots > X*100\), in which all calculations are of integers.

Sample Code (C)

#include<stdio.h>

int main(){
	int n,x;
	scanf("%d%d",&n,&x);
	int sum=0;
	for(int i=0;i<n;i++){
		int v,p;
		scanf("%d%d",&v,&p);
		sum+=v*p;
		if(sum>x*100){
			printf("%d\n",i+1);
			return 0;
		}
	}
	puts("-1");
}

Sample Code (Python)

N,X = map(int,input().split())
s = 0

for i in range(N):
  v,p = map(int,input().split())
  s += v*p
  if s > X*100:
    print(i+1)
    exit()

print(-1)