#include <stdio.h>

int main() {
    int n;
    int q;
    int data[50005];
    scanf("%d %d", &n, &q);

    for (int i = 1; i <= n; i++) {
        scanf("%d", &data[i]);
    }

    for (int i = 0; i < q; i++) {
        int a, b;
        double total = 0;
        
        scanf("%d %d", &a, &b);

        for (int j = a; j <= b; j++) {
            total = total + data[j];
        }

        int jumlah_hari = b - a + 1;
        double rata = total / jumlah_hari;

        printf("Hari ke %d-%d: %.2f\n", a, b, rata);
    }

    return 0;
}