#include <stdio.h>
int main()
{
int i,j;
char str[1000];
scanf("%s",str); // input the string
for (i = 0; str[i] != '\0'; i++)
{
for (j = i + 1; str[j] != '\0'; j++)
{
if (str[i] == str[j]) // compare
{
printf("%c", str[i]);
return 0;
}
}
}
}
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