function Main(input) {
  input = input.split("\n");
  var N = input[0];
  var S = input[1].split("");
  var sum = 0;
  for(var i=1;i<1000;i++){
    var count = 0;
    if(i<10){
    var io = "00"+i;
    }else if(i<100){
    var io = "0"+i;
    }else{
    var io = ""+i;
    }
    for(var j=0;j<N;j++){
      switch(count){
        case 0:
          if(S[j]==io.slice(0,1)){
            count++;
          }
        break;
        case 1:
          if(S[j]==io.slice(1,2)){
            count++;
          }
        break;
        case 2:
          if(S[j]==io.slice(2,3)){
            count++;
          }
          break;
        }
        if(count == 3){
          sum++;
          break;
        }
      }
    }
console.log(sum);
}Main(require("fs").readFileSync("/dev/stdin", "utf8"));