"use strict";
const Main = (input) =>{
   let xs = input.trim().split('\n');
   let N = xs[0].trim().split('');
   let A = xs[1].trim().split('');
   let B = xs[2].trim().split('');
   let C = xs[3].trim().split('');
   let count = 0;
   for(let i=0; i<N; i++){
     if(A[i]==B[i]&&B[i]==C[i]){
     count +=0;
     }else if(A[i]==B[i]||A[i]==C[i]||B[i]==C[i]){
     count +=1;
     }else{
     count +=2;
     }
   }
   console.log(count);

}
Main(require('fs').readFileSync('/dev/stdin','utf8'));