#include <stdio.h>
#include <stdlib.h>

double meanAriphm(FILE* f);

int main() {
    FILE* in = fopen("input.txt", "r");
    if (in == NULL) {
        perror("Could not open input file");
        return (-1);
    }

    double m = meanAriphm(in);
    fclose(in);

    FILE* out = fopen("output.txt", "w");
    if (in == NULL) {
        perror("Could not open output file");
        return (-1);
    }

    fprintf(out, "%f\n", m);
    fclose(out);
    return 0;
}

double meanAriphm(FILE* f) {
    int n = 0;
    double sum = 0.;
    double a;
    while (fscanf(f, "%lf", &a) == 1) {
        sum += a;
        ++n;
    }
    if (n == 0) {
        fprintf(stderr, "Incorrect file format.\n");
        exit(-1);
    }
    return sum / (double) n;
}