C++ :

#include<bits/stdc++.h>
using namespace std;
string s1="abcdefghijklmnopqrstuvwxyz",s;
int ans;
int main()
{
	cin>>s;
	s+='!';
	for(int i=0;i<s.size();i++)
		if(s[i]!=s1[i]) {
			cout<<i;
			return 0;
		}
}