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

int main(int argc, char **argv) {

    // Get filename as an argument, defaults to "input.txt"
    char *path = (argc > 1) ? argv[1] : "input.txt";

    if (!path)
    {
        printf("Requires input file.\n");
        return 1;
    }

    FILE *file = fopen(path, "r");

    if (!file)
    {
        printf("Could not find file.");
        return 1;
    }

    int8_t firstdigit = -1;
    int8_t lastdigit = -1;
    uint32_t sum = 0;
    char current = 0;

    while (current != EOF)
    {
        current = fgetc(file);

        if (current == '\n')
        {
            if (lastdigit == -1) lastdigit = firstdigit;
            sum += (firstdigit * 10) + lastdigit;
            firstdigit = -1;
            lastdigit = -1;
            continue;
        }

        if (current < '0' || current > '9') continue;

        if (firstdigit == -1)
        {
            firstdigit = current - '0';
        }
        else
        {
            lastdigit = current - '0';
        }
    }

    printf("Sum: %d\n", sum);

    return 0;
}