#include <stdio.h>
#include <ctype.h>
#include <string.h>

int myatoi(char *instr) {
    int sign = 1;
    if (*instr == '-') {
        sign = -1;
        instr++;
    }

    for (; *instr != '\0'; instr++) {
        if (!isdigit(*instr)) {
            return 0;
        }
    }

    int num = 0;
    instr -= strlen(instr);

    while (*instr >= '0' && *instr <= '9') {
        num = num * 10 + (*instr - '0');
        instr++;
    }

    return num * sign;
}

int main() {
    char input[] = "-2890";
    int number = myatoi(input);
    printf("Converted number is: %d\n", number);

    char bad_input[] = "2890kjdfshdfsh";
    number = myatoi(bad_input);
    printf("Bad input result: %d\n", number);

    return 0;
}