#include <ctype.h>
#include <stdlib.h>

/*
** atoi(s) - convert s to integer.
*/
int atoi(const char* s)
{
    int sign, n;
    while (isspace(*s))
        ++s;
    sign = 1;

    switch (*s) {
    case '-':
        sign = -1;
    case '+':
        ++s;
    }

    n = 0;
    while (isdigit(*s))
        n = 10 * n + *s++ - '0';
    return (sign * n);
}