#include <stdio.h>
#include <math.h>
#define MAXLEN 1000

/* convert hex to decimal */

main()
{
    char input[MAXLEN];
    printf("Hex number: 0x");
    printf("Decimal conversion: %d\n", htoi(input));
    return 0;
}

int htoi(char s[])
{
    int i, c, num, dec, res;

    res = 0;
    for (i=0; i<MAXLEN-1 && (c=getchar())!=EOF && c!='\n'; ++i)
        s[i] = c;
    num = i;
    ++i;
    s[i] = '\0';
    i = 0;
    for (num; num > 0; --num) {
        if (s[i] >= 'A' && s[i] <= 'F')
            dec = toupper(s[i]) - 'A' + 10;
        else if (s[i] >= '0' && s[i] <= '9')
            dec = s[i] - '0';
        else
            dec = 0;
        res = res + (double) pow(16, (num-1)) * dec;
        ++i;
    }
    return res;
}