#include <stdio.h>

int main() {
	int data[9] = {10, 15, 15, 18, 20, 20, 20, 25, 30};
	int A = 15;
    int B = 20;
	int low,high,mid;
    int resultA = 0;
    int resultB = 0;
    
	low = 0;
	high = 9;
    while(low < high){
        mid = (low + high) / 2;
        if (data[mid] >= A){
            high = mid;
        }else{
            low = mid +1;
        }
    resultA = low;
}

    low = 0;
	high = 9;
    while(low < high){
        mid = (low + high) / 2;
        if (data[mid] > B){
            high = mid;
        }else{
            low = mid +1;
        }
    resultB = low;
}
    
    printf("%d",resultB-resultA);
    return 0;
}