#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,m=0;
	cin>>n;
	string a;
	cin>>a;
	for(int i=0;i<n-1;i++)
	{
		if(a[i]=='V'&&a[i+1]=='K')
		{
			m++;
			a[i]='x';
			a[i+1]='x';
		}
		if(a[i]=='V'&&a[i+1]=='V')
		{
			m++;
		}
		if(a[i]=='K'&&a[i+1]=='K')
		{
			m++;
		}
	}
	if(m==0)cout<<"-1";
	else cout<<m;
	return 0;
 }