#include <stdio.h>

int main() {
	int data[4] = {10, 15, 17, 20};
	int target = 7;
	int low,high;
	low = 1;
	high = 20;
    int result = -1;
    while(low <= high){
        int mid = (low + high) / 2;
        int sum = 0;
        for (int i = 0;i < 4;i++) {
            if (data[i] > mid) {
               sum += data[i] - mid; 
            }
        }
        
        if (sum >= target) {
            result = mid;
            low = mid + 1;
        }else{
            high = mid -1;
        }
    }
    printf("%d ",result);
	return 0;
}